Method for selecting formulations to treat electrical cables

ABSTRACT

A method for selecting components for a mixture to be injected into an interstitial void volume adjacent to a central stranded conductor of an electrical cable segment having the central conductor encased in a polymeric insulation jacket to enhance the dielectric properties of the cable segment. The method includes selecting an anticipated operating temperature for the cable segment to be used in selecting the components for the mixture to be injected into the interstitial void volume of the cable segment and selecting a minimum desired time period to be used in selecting the compounds for the mixture to be injected during which the dielectric properties of the cable segment are to be enhanced by the mixture. Next, first, second and third components for the mixture are selected to provide the cable segment with a reliable life at the selected operating temperature spanning first, second and third time periods, respectively.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method for enhancing the dielectricstrength of an electrical power cable and, more particularly, relates toan efficient and effective method for selecting formulations to treatelectrical cable segments.

2. Description of the Related Art

Extensive networks of underground electrical cables are in place in manyparts of the industrialized world. Such underground distribution offersgreat advantage over conventional overhead lines in that it is notsubject to wind, ice or lightning damage and is thus viewed as areliable means for delivering electrical power without obstructing thesurrounding landscape, the latter feature being particularly appreciatedin suburban and urban settings. Unfortunately, these cables, whichgenerally comprise a stranded conductor surrounded by a semi-conductingshield, a layer of insulation jacket, and an insulation shield, oftensuffer premature breakdown and do not attain their originallyanticipated longevity of 30 to 40 years. Their dielectric breakdown isgenerally attributed to at least two so-called “treeing” phenomena whichlead to a progressive degradation of the cable's insulation. The first,“electrical treeing,” is the product of numerous electrical dischargesin the presence of strong electrical fields which eventually lead to theformation of microscopic branching channels within the insulationmaterial, from which the descriptive terminology derives. A similarmechanism, “water treeing,” is observed when the insulation material issimultaneously exposed to moisture and an electric field. Although thelatter mechanism is much more gradual than electrical treeing, it doesoccur at considerably lower electrical fields and therefore isconsidered to be a primary contributor to reduced cable service life.Since replacing a failed section of underground cable can be a verycostly and involved procedure, there is a strong motivation on the partof the electrical utility industry to extend the useful life of existingunderground cables in a cost-effective manner.

Two early efforts by Bahder and Fryszczyn focused on rejuvenatingin-service cables by either simply drying the insulation or introducinga certain liquid into the void volume associated with the conductorgeometry after such a drying step. Thus, in U.S. Pat. No. 4,545,133 theinventors teach a method for retarding electrochemical decomposition ofa cable's insulation by continuously passing a dry gas through theinterior of the cable. Only nitrogen is explicitly recited as the gas tobe used and maximum pressure contemplated for introducing the gas is 50psig (pounds per square inch above atmospheric pressure). Not only isthis method cumbersome, but it requires extensive monitoring andscheduled replenishment of the dry gas supply. U.S. Pat. No. 4,372,988to Bahder teaches a method for reclaiming electrical distribution cablewhich comprises drying the cable and then continuously supplying a treeretardant liquid to the interior of the cable. The liquid was believedto diffuse out of the cable's interior and into the insulation, where itfilled the microscopic trees and thereby augmented the service life ofthe cable. This disclosure suffers from the disadvantage that theretardant can exude or leak from the cable. The loss of liquid wasaddressed by a preferred embodiment wherein external reservoirs suitablefor maintaining a constant level of the liquid were provided, furtheradding to the complexity of this method.

An improvement over the disclosure by Bahder was proposed by Vincent etal. in U.S. Pat. No. 4,766,011, wherein the tree retardant liquid wasselected from a particular class of aromatic alkoxysilanes. Again, thetree retardant was supplied to the interstices of the cable conductor.However, in this case, the fluid can polymerize within the cable'sinterior as well as within the water tree voids in the insulation andtherefore does not leak out of the cable, or only exudes therefrom at alow rate. This method and variations thereof employing certain rapidlydiffusing components (see U.S. Pat. Nos. 5,372,840 and 5,372,841) haveenjoyed commercial success over the last decade or so, but they stillhave some practical limitations when reclaiming underground residentialdistribution (URD) cables, which have a relatively small diameter, andtherefore present insufficient interstitial volume relative to theamount of retardant required for optimum dielectric performance. Thus,although not explicitly required by the above mentioned disclosures, atypical in-the-field reclamation of URD cables employing suchsilane-based compositions typically leaves a liquid reservoir connectedto the cable for a 60 to 90 day “soak period” to allow sufficientretardant liquid to penetrate the cable insulation and thereby restorethe dielectric properties. For example, cables having round conductorssmaller than 4/0 (120 mm²) generally require the above describedreservoir and soak period to introduce a sufficient amount of treatingfluid. In reality, this is an oversimplification, since some cableslarger than 4/0 with compressed or compacted strands would suffer fromthe same inadequate fluid supply. As a result, it is generally necessaryto have a crew visit the site at least three times: first to begin theinjection which involves a vacuum at one end and a slightly pressurizedfeed reservoir on the other end, second to remove the vacuum bottle afew days later after the fluid has traversed the length of the cablesegment, and finally to remove the reservoir after the soak period iscomplete. The repetitive trips are costly in terms of human resource.Moreover, each exposure of workers to energized equipment presentsadditional risk of serious injury or fatality and it would be beneficialto minimize such interactions. In view of the above limitations, acircuit owner might find it economically equivalent, or evenadvantageous, to completely replace a cable once it has deterioratedrather than resort to the above restorative methods.

Unlike the above described URD systems, large diameter (e.g., feeder)cables present their own unique problems. Because of the relativelylarger interstitial volumes of the latter, the amount of retardantliquid introduced according to the above described methods can actuallyexceed that required to optimally treat the insulation. Such systems donot require the above described reservoir, but, as the temperature ofthe treated cable cycles with electrical load, thermodynamic pumping ofever more liquid from the cable's core into the insulation was believedto be responsible for the catastrophic bursting of some cables. This“supersaturation” phenomenon, and a remedy therefor, are described inU.S. Pat. No. 6,162,491 to Bertini. In this variation of the abovedescribed methods, a diluent, which has a low viscosity, is insoluble inthe insulation and is miscible with the retardant liquid, is added tothe latter, thereby limiting the amount of retardant which can diffuseinto the insulation. A methodology for determining the proper amount ofthe diluent for a given situation is provided. While this method mayindeed prevent the bursting of large cables after treatment it does nottake advantage of the extra interstitial volume by employing a diluentwhich is incapable of providing any benefit to the long-term dielectricperformance of the insulation. Thus, this method does not take advantageof the large interstitial volume associated with such cables.

In all of the above recited methods for treating in-service cables, theretardant liquid is injected into the cable under a pressure sufficientto facilitate filling the interstitial void volume. But, althoughpressures as high as 400 psig have been employed to this end (e.g.,Transmission & Distribution World, Jul. 1, 1999, “Submarine CableRescued With Silicone-Based Fluid”), the pressure is always discontinuedafter the cable is filled. At most, a residual pressure of up to 30 psigis applied to a liquid reservoir after injection, as required for thesoak period in the case of URD cable reclamation. And, while relativelyhigh pressures have been used to inject power cables, this prior use issolely to accelerate the cable segment filling time, especially for verylong lengths as are encountered with submarine cables (the aboveTransmission & Distribution World article), and the pressure wasrelieved after the cable segment was filled. Furthermore, even whenhigher pressures were maintained in an experimental determination ofpossible detrimental effects of excessive pressure, the pressure wasmaintained for only a brief period by an external pressure reservoir tosimulate the injection of longer segment lengths than those employed inthe experiment (“Entergy Metro Case Study: Post-Treatment Lessons,” GlenBertini, ICC April, 1997 Meeting, Scottsdale, Ariz.). In this case, evenafter two hours of continuous pressure at 117 psig, the interstitialvoid volume of the cable segment was not completely filled and it wassuggested that the inability to completely fill the interstices was dueto severe strand compaction.

While injection to extend the life of power cables has been inwide-spread use for two decades, in each case a single activeformulation (either an essentially pure compound or a mixture) is pumpedinto cables to extend life (see U.S. Pat. Nos. 4,372,988; 4,766,011;5,372,840 and 5,372,841). While each of these prior art patents suggeststhat mixtures of materials might be efficacious, they do not suggest amethod to optimize the total quantity and total concentration of eachcomponent in a mixture to match the unique geometry, condition, andanticipated operation of each cable. In some cases, where there arelarger conductors with less severe compaction, there may be moreinterstitial volume available within the strand interstices thanrequired to treat the cable. The prior art approach does disclose theaddition of non-active dilutants to mitigate potential conditions ofsuper saturation (see U.S. Pat. No. 6,162,491). But, in each and everycase a single formulation of active ingredients is utilized.

BRIEF SUMMARY OF THE INVENTION

A method for selecting components for a mixture to be injected into aninterstitial void volume adjacent to a central stranded conductor of anelectrical cable segment having the central conductor encased in apolymeric insulation jacket to enhance the dielectric properties of thecable segment. The method includes selecting an anticipated operatingtemperature for the cable segment to be used in selecting the componentsfor the mixture to be injected into the interstitial void volume of thecable segment; and selecting a minimum desired time period to be used inselecting the compounds for the mixture to be injected into theinterstitial void volume of the cable segment during which thedielectric properties of the cable segment are to be enhanced by themixture. Next, the method includes selecting a first component for themixture to provide the cable segment with a reliable life at theselected operating temperature spanning a first time period; selecting asecond component for the mixture to provide the cable segment with areliable life at the selected operating temperature spanning a secondtime period at least in part extending beyond the first time period; andselecting a third component for the mixture to provide the cable segmentwith a reliable life at the selected operating temperature spanning athird time period at least in part extending beyond the second timeperiod and beyond the minimum desired time period. In another aspect, amethod is provided for making a mixture to be injected into theinterstitial void volume of the cable segment including selecting theanticipated operating temperature and the minimum desired time period asnoted above, and also selecting a desired quantity of the mixture to beinjected into the interstitial void volume of the cable segment to atleast fill the interstitial void volume, selecting first, second andthird components for the mixture in first, second and third quantities,respectively, to produce at least the desired quantity of the mixture tobe injected into the interstitial void volume, with: the first componentfor the mixture and the first quantity of the first component to beincluded in the mixture being further selected so as to provide thecable segment with a reliable life at the selected operating temperaturespanning a first time period, the second component for the mixture andthe second quantity of the second component to be included in themixture being further selected so as to provide the cable segment with areliable life at the selected operating temperature spanning a secondtime period at least in part extending beyond the first time period, andthe third component for the mixture and the third quantity of the thirdcomponent to be included in the mixture being further selected so as toprovide the cable segment with a reliable life at the selected operatingtemperature spanning a third time period at least in part extendingbeyond the second time period and beyond the minimum desired timeperiod. The method further including mixing the first, second and thirdquantities of the first, second and third components together.

Other features and advantages of the invention will become apparent fromthe following detailed description, taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)

FIG. 1 is a plot of actual measured weight (top curve), and calculatedweight (bottom curve), of acetophenone injected into a cable segment asa function of injection pressure, the respective weights beingnormalized to a 1000 foot cable length.

FIG. 2 is a plot of the pressure decay observed as a function of timeafter the cable segment of FIG. 1 was filled and the acetophenoneconfined under the indicated pressures.

FIG. 3 is a cross-sectional view of a high-pressure terminal connectorused to inject acetophenone into the cable segment of FIG. 1.

FIG. 3A is plan view of the washer of FIG. 3 and associated set-screws.

FIG. 4 is a perspective view of the assembled connector of FIG. 3showing use of a split ring collar.

FIG. 5 is a partial cross-sectional view of a swagable high-pressure,integral housing terminal connector having machined teeth in the swagingregions.

FIG. 6 is an enlarged, cross-sectional view of the self-closingspring-actuated injection valve of FIG. 5 showing an associatedinjection needle used to supply fluid to the high-pressure terminalconnector.

FIG. 7 is a partial cross-sectional view of a swagable high-pressure,dual-housing splice connector having machined teeth in the swagingregions.

FIG. 8 is a schematic diagram summarizing methodology and variables ofthe present invention.

FIG. 9 is a graph of diffusion coefficients in polyethylene ofphenylmethyldimethoxysilane and oligomeric condensation products thereofas a function of temperature.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is directed to a method for selecting formulationsto treat electrical cables. However, before discussing that method, aninventive method used for enhancing the dielectric properties of anin-service electrical power cable segment having a central strandedconductor, usually surrounded by a semi-conducting strand shield, andencased in a polymeric insulation, with an interstitial void volume inthe region of the conductor, which is the preferred method for applyingthe formulations selected using the method of the present invention,will be discussed in detail. The method for enhancing the cable segmentinvolves filling the interstitial void volume with at least onedielectric property-enhancing fluid at a pressure below the elasticlimit of the polymeric insulation jacket, and subsequently confining thedielectric property-enhancing fluid within the interstitial void volumeat a desirable sustained residual pressure imposed along the entirelength of the cable segment and, again, below the elastic limit. Themethod for enhancing the cable segment exploits the discovery that, whenthe interstitial void volume of a cable segment is filled with adielectric property-enhancing fluid and the fluid confined therein at ahigh residual pressure, the volume of fluid actually introducedsignificantly exceeds the volume predicted from a rigorous calculationof the cable's expansion at the imposed pressure. The difference betweenthe observed and calculated volume change increases with pressure and isbelieved to be due mainly to the accelerated adsorption of the fluid inthe conductor shield as well as transport thereof through the conductorshield and insulation of the cable. Thus, with sufficient residualsustained pressure, it is possible to expand the insulation jacket of anin-service cable segment in a manner that is so slight as to not causeany mechanical damage to the cable or to induce any untoward electricaleffects, yet large enough to significantly increase the volume ofdielectric property-enhancing fluid which can be introduced. As aresult, and unlike the prior art, the present method does not requirethe above mentioned “soak” period, and the associated external pressurereservoir, to introduce a sufficient amount of fluid to effectivelytreat the cable segment. As used herein, the term “elastic limit” of theinsulation jacket of a cable segment is defined as the internal pressurein the interstitial void volume at which the outside diameter of theinsulation jacket takes on a permanent set at 25° C. greater than 2%(i.e., the OD increases by a factor of 1.02 times its original value),excluding any expansion (swell) due to fluid dissolved in the cablecomponents. This limit can, for example, be experimentally determined bypressurizing a sample of the cable segment with a fluid having asolubility of less than 0.1% by weight in the conductor shield and inthe insulation jacket (e.g., water), for a period of about 24 hours,after first removing any covering such as insulation shield and wirewrap, after the pressure is released, the final OD is compared with theinitial OD in making the above determination. For the purposes herein,it is preferred that the above mentioned residual pressure is no morethan about 80% of the above defined elastic limit.

The in-service cable segment to which the present methods discussed aregenerally applied is the type used in underground residentialdistribution and typically comprises a central core of a stranded copperor aluminum conductor encased in a polymeric insulation jacket. Thestrand geometry of the conductor defines an interstitial void volume. Asis well known in the art, there is usually also a semi-conductingpolymeric conductor shield positioned between the conductor andinsulation jacket. However, this shield can also be of a highpermittivity material sometimes utilized in EPR cables. Further, lowvoltage (secondary) cables do not employ such a shield. In addition, thecables contemplated herein often further comprise a semi-conductinginsulation shield covering the insulation jacket, the latter beingordinarily wrapped with a wire or metal foil grounding strip and,optionally, encased in an outer polymeric, metallic, or combination ofmetallic and polymeric, protective jacket. The insulation material ispreferably a polyolefin polymer, such as high molecular weightpolyethylene (HMWPE), cross-linked polyethylene (XLPE), a filledcopolymer or rubber of polyethylene and propylene (EPR), vinyl acetateor is a solid-liquid dielectric such as paper-oil. The base insulationmay have compounded additives such as anti-oxidants, tree-retardants,plasticizers, and fillers to modify properties of the insulation. Mediumvoltage, low voltage and high voltage cables are contemplated herein. Asused herein, the term “in-service” refers to a cable segment which hasbeen under electrical load and exposed to the elements for an extendedperiod. In such a cable, the electrical integrity of the cableinsulation has generally deteriorated to some extent due to theformation of water trees, as described above. It is also contemplated,however, that the method discussed can be used to enhance the dielectricproperties of a new cable as well as an in-service cable. For thepurposes herein, “sustained pressure” indicates that the fluid iscontained or trapped within a cable segment's interstitial void volumeat the residual pressure after the pressurized fluid source is removed,whereupon the pressure decays only by subsequent permeation through theconductor shield and insulation, as described infra. The method forenhancing the cable segment to be first discussed teaches therelationship between pressure and the augmented injection volume undersustained residual pressure and demonstrates the feasibility ofeliminating or reducing the soak phase on cables with small conductors.

The above observations were made as follows. Nominal 100 foot longcoiled cable segments (1/0, 175 mil, XLPE; cross-linked polyethyleneinsulation) were injected with acetophenone at sustained pressures of30, 60, 120, 240, and 480 psig (pounds per square inch, gage) while thesegments were immersed in water at 30° C. using novel high-pressureterminal connectors described infra. At each pressure, the outsidediameter (OD) of the insulation was measured and compared to the ODbefore the cable was pressurized (i.e., 0 psig). The changes in the ODwere monitored at each cable end and four individual measurements (twoorthogonal measurements on each end of each cable segment) were averagedat each pressure, the repeatability of each individual measurement beingapproximately +/−2 mils. These increases in OD were plotted as afunction of pressure, but the theoretically expected linear relationshipwas not observed due to the relatively high error of OD measurement atlow pressures. Therefore, the high pressure point (approximately 480psig) was used to fit a rigorous equation relating OD change(deflection) to internal pressure of an annulus, the latter being a veryclose approximation of the cable's geometry (e.g., see Jaeger & Cook,Fundamentals of Rock Mechanics, 2^(nd) edition, p. 135) according to thefollowing equations: $\begin{matrix}{{{{Lame}'}s\quad{parameters}\quad G}:={{\frac{E}{2 \cdot \left( {1 + v} \right)}\quad G} = {8.6\quad{ksi}}}} \\{\quad{\lambda:={{\frac{E \cdot v}{\left( {1 + v} \right) \cdot \left( {1 - {2 \cdot v}} \right)}\quad\lambda} = {98\quad{ksi}}}}} \\{{Radial}\quad{deflection}\quad{at}\quad{any}\quad{radius}\quad{with}\quad{internal}\quad{pressure}} \\{{only},{{{Ref}.\quad{Fundamentals}}\quad{of}\quad{Rock}\quad{Mechanics}},} \\{{{{Jaeger}\&}\quad{Cook}},{2{nd}\quad{{Ed}.}},{p{.135}}} \\{{u(r)}:={\frac{{- p_{i}} \cdot a^{2} \cdot r}{2 \cdot \left( {\lambda + G} \right) \cdot \left( {b^{2} - a^{2}} \right)} - \frac{p_{i} \cdot a^{2} \cdot b^{2}}{2 \cdot G \cdot \left( {b^{2} - a^{2}} \right) \cdot r}}}\end{matrix}\quad$wherein E is the elastic modulus and v is Poison's ratio for the cableinsulation, u (r)=radial deflection at a given radius r, a=inner radius,b=outer radius, G=shear modulus, λ=Lame's parameter, p_(i)=pressure inthe interstices, and “ksi” indicates units in kilo-pounds per squareinch. The increase in OD at 480 psig was first determined to beapproximately 9.1 mils (1 mil= 1/1000 in.), or 1.2% of the initial OD of0.78 in. The modulus E was adjusted so as to correspond to this measuredOD deflection using the known value of v=0.46 for the insulation (E=19kpsi). From this, the change of the inner diameter (ID) was calculatedas 18.2 mil. A similar procedure was used to calculate the change in IDas a function of pressure. Thus, at 480 psig, the increase in ID createdan incremental annular void volume between the conductor strands and theconductor shield which corresponds to the introduction of approximately4.5 pounds of acetophenone per 1000 feet of cable beyond the amount thiscable can accommodate at atmospheric pressure, the latter amount beingabout 5.2 pounds per 1000 feet including the negligible compressibilityof acetophenone. The resulting hydraulic expansion translates into,e.g., an 87% increase in total void volume at 480 psig, and it alonecould eliminate the soak phase required by the prior art methods forsome cables having insufficient interstitial void volume (e.g., thosehaving a ratio of v₁ to v₂ in Table 1 of U.S. Pat. No. 6,162,491 lessthan unity). The calculated increase in fluid accommodated as a functionof applied pressure for the above cable, expressed in pounds/1000 feet(lb/kft) of cable and normalized to a specific gravity (SG) of 1.0, isrepresented by the lower curve of FIG. 1.

In a similar fashion, the actual total volume (weight) introduced intothe cable as a function of pressure was determined as follows. A 107foot length of the above mentioned I/O cable was fitted with the novelhigh-pressure connector, described infra, at each terminus. A fluidreservoir and positive displacement pump were attached to the firstconnector via a closable valve and acetophenone was injected into thecable until fluid was observed to flow from the opposite end while thecable was maintained at 30° C. in a water bath. At this point, a valveattached to the second connector was closed and pumping was continueduntil the pressure reached the desired level (e.g., the above mentioned480 psig), at which time the valve on the first connector was shut tocontain the pressurized fluid, this sequence taking approximately 15 to30 minutes for each target pressure. The amount of fluid so injectedinto the interstitial void volume of the cable segment was determined byweighing the reservoir before and after injection as well as by notingthe amount of fluid displaced by the pump, these two close measurementsthen being averaged. Of course, any possible leakage from the cable wasruled out. As above, this measurement was normalized to SG=1.0 for a1000 foot cable to provide a basis for comparison of the various cablessamples. Unexpectedly, the actual total amount of acetophenone whichcould be introduced into the interstitial void volume of the above cableat 480 psig was found to be considerably greater than the abovegeometrically predicted value of 87%. For example, when confined withinthe cable interior at 480 psig, the incremental amount of this fluid was9.4 lb/kft greater than the zero pressure value of 5.2 lb/kft, or 180%of the zero-pressure interstitial volume (weight) and the total fluidaccommodated was 5.2+9.4=14.6 lb/kft at 480 psig. It was verified thatno leakage of fluid took place. Measurements at other pressures arerepresented by the upper curve of FIG. 1 (again normalized to SG=1.0),wherein the difference between the actual amount accommodated at a givenpressure and the amount predicted from the above describe geometriccalculations is termed the “Permeation-Adsorption Gap.” This gap widenedwith increasing pressure over the range studied.

The effect of fluid compressibility can be readily estimated and largelydiscounted as insignificant in the above experiment. For example, thecompressibility of benzene, a material similar to acetophenone, is6.1×10⁻⁶ ΔV/V·psi. At a nominal pressure of 480 psig, benzene would becompressed only about 0.3%. Thus, even fluids having highcompressibility, such as silicones, would introduce no more than about0.5 to 1% of additional fluid at the maximum pressures contemplatedherein, an amount insignificant relative to the increases observed.

While not wishing to be limited to any specific mechanism, it isbelieved that the above described dramatic increase in effectiveinterstitial void volume (or injection volume) is due, at least in part,to the heterogeneous and micro-porous nature of the conductor shield.This shield is typically a polyolefin polymer filled with 28-40% carbonblack. Carbon black, which is added primarily to impart semi-conductingproperties to the conductor shield, contains microscopic surfaceirregularities which make it an excellent adsorption surface for thedielectric property-enhancing fluid. It is believed that fluids injectedat high pressure essentially flow through these microscopic surfaces andchannels faster than if they were injected at a lower pressure. Furtherit is believed that a substantial portion of the fluid can be reversiblyadsorbed onto the carbon black surface (i.e., into the conductorshield), thereby providing another reservoir to store the dielectricproperty-enhancing fluid.

Besides the advantage of creating a larger “internal reservoir,” oneskilled in the art would recognize another advantage of this rapidradial transport through the conductor shield. Rapid delivery ofdielectric property-enhancing fluid to the conductor shield/insulationinterface where dielectric degradation has occurred is a desirableoutcome not enjoyed by the prior art approaches. Rapid increase ofdielectric performance is critical for good reactive injectionperformance (i.e., treatment after a cable failure). As discussed above,the elevated injection pressures occasionally utilized in the prior artare released as soon as the fluid reaches the far end of the cablesegment being injected. Using this conventional mode of operation, thesegment end adjacent to the pressure source receives a small benefit,but the distal end receives no benefit since it remains at near ambientpressure throughout the injection process. By analogy to a chain whichfails at its weakest link, any restoration process which does notbenefit the whole cable segment provides virtually no benefit since acable failure anywhere along the length causes the entire length tobecome non-functional. Again, the low to moderate pressures used in theart today (10-350 psig) are lower than the maximum pressurescontemplated by the present method (i.e., up to about 1000 psig) and,most significantly, are bled to near zero (e.g., nominal soak pressureless than 30 psig and more typically less than 10 psig, using anexternal reservoir) after the fluid has flowed the length of the cable.Thus, for example, while the above mentioned I/O cable segment having alength of 100 to 300 feet can be injected in only about 10 to 30 minutesto raise the interstitial pressure throughout to 480 psig, the presentmethod holds such pressures throughout the entire cable length for days,or weeks, or months after the injection is complete.

Another advantage of the method for enhancing the cable segment firstbeing discussed is that it accelerates the diffusion of the dielectricproperty-enhancing fluid through the insulation jacket of the cablesegment, this being verified as follows. In a manner similar to theabove described experiments, three identical I/O cable segments havinglengths ranging from approximately 105.5 to 107 feet were injected withacetophenone at 30, 240, and 480 psig at 30° C. After the cables werefilled, pressure was maintained for 30 minutes to simulate a typicalinjection condition contemplated by the present method. After the 30minute interval, the fluid feed was terminated by closing a valve at thefeed point to the cable and the respective pressure was allowed to decaywith time as fluid permeated out of the interstitial volume and into theconductor shield and insulation (but not by leaking from theconnectors). The results of that pressure decay for only the two higherpressures are plotted in the FIG. 2, the decay for the 30 psig cablebeing very rapid and reaching approximately 0 psig within about one day.Again, while not wishing to be constrained by any particular theory, itis believed that the initial rapid decrease of pressure, which was morerapid with greater applied pressure, results from the transport of fluidfrom the interstices into the conductor shield. After this rapid,initial phase, and as the conductor shield becomes saturated with thefluid, the pressure decays at a considerably reduced rate. This phase isbelieved to be due to the permeation of additional fluid out of theinterstitial void volume and into the insulation.

In the above experiments, the novel high-pressure connector 250, shownin cross-sectional view in FIG. 3, was used to fill the test cables atelevated pressure. In a typical assembly and test procedure, the cabletermination was prepared by cutting back the outermost layers of the I/Ocable to expose insulation jacket 12, per the manufacture'srecommendations. Likewise, insulation jacket 12 and associated conductorshield (not shown) were cut back slightly beyond the manufacturer'srequirements to expose stranded conductor 14 and assure that there wasat least a 0.25 inch gap between termination crimp connector 252 and thewall of insulation jacket 12 after termination crimp connector 252 wascrimped to the conductor 14. After the crimping procedure was complete,a first threaded cap 210 was installed over the insulation jacket 12followed by first aluminum washer 212, rubber washer 214, and a secondaluminum washer 212. The cable-side threaded housing 220 was thenloosely threaded onto the already installed first threaded cap 210 atthe right side of high-pressure terminal connector 250. The rubberO-ring 216 was installed in a groove of the termination-side threadedhousing 218 and the latter was, in turn, threaded onto the cable-sidethreaded housing 220 until the external gap between the two housingcomponents was essentially closed. It should be apparent to someone withordinary skill that housings 218 and 220 could be reversed in the abovedescription with no impact. An aluminum washer 226, having associatedset screws 228 and illustrated in detail in FIG. 3A, was slid intoposition so as to reside over the smooth surface of termination crimpconnector 252. While the assembly up to this point was slid slightlytoward the cable side, two or three set screws were engaged so thataluminum washer 226 was immobilized with respect to the terminationcrimp connector 252. The position was chosen so that the rubber washer224, which was added next, fell squarely on the un-crimped cylindricalsurface of termination crimp connector 252 when the assembly wascompleted. At this point, the partially assembled high-pressureconnector could be slid back toward the termination side to the positionshown in FIG. 3. Aluminum washer 222 was placed adjacent to the rubberwasher 224, a second threaded cap 210 was mated with thetermination-side threaded housing 218 and threaded tightly thereto. Theresulting compression provided sufficient force to deform rubber washer224 to make a fluid-tight seal with respect to termination crimpconnector 252 and the inside diameter of the termination-side threadedhousing 218. The threads on the cable-side housing 220 were thentightened firmly such that the rubber washer 214 was compressed betweenthe two aluminum washers 212, the compression providing sufficient forceto deform rubber washer 214 to make a fluid-tight seal with respect tothe surface of insulation jacket 12 and the inner peripheral surface ofthe cable-side threaded housing 220.

A split ring clamping collar 230, comprising two halves 232 and 234,each half having course internal threads 231 for engaging and graspinginsulation jacket 12, was placed in the approximate position shown inFIG. 3 and in perspective view in FIG. 4. A hose clamp was used totemporarily hold the two halves of the collar 230 in place while twoclamping collar bolts 238 were inserted and threaded into the firstthreaded cap 210 and partially tightened. The hose clamp was thenremoved and two clamping collar chord bolts 241 were screwed tightlyinto place to permanently join the two halves 232 and 234 of clampingcollar 230, and collar bolts 238 were then completely tightened. As aresult, the rough threads 231 disposed on the inner diameter of collar230 partially penetrated or deformed the surface of insulation 12 so asto provide resistance to axial movement of connector 250 relative to theinsulation jacket 12 of the cable segment to be injected under pressure.It was previously determined that, without such a means for securing theinsulation jacket to the high-pressure connector, a “pushback”phenomenon resulted. Pushback is defined herein as the axial movement orcreep of the insulation jacket and conductor shield away from the cutend (crimped end) of the conductor of a cable segment when a fluid isconfined within its interstitial void volume at a high residualpressure. Ultimately, this pushback phenomenon resulted in sufficientdisplacement of the insulation jacket 12 relative to the above describedcompression seal 212/214/212 to cause fluid to leak from the connectionand the high residual pressure to quickly collapse, thereby destroyingthe intent of the instant method. Acetophenone was then injected orwithdrawn through one of the threaded injection ports 240 or 242 usingan NTP to tube fittings well known in the art, as described above. Theunused threaded injection port was plugged with a threaded plug (notshown). The inventors of the instant application developed theabove-described high-pressure power cable connector and other connectorsfor use with the method for treating electrical cables at sustainedelevated pressure described herein. Such high-pressure connectors aredescribed in detail in Provisional patent application Method forTreating Electrical Cable at Sustained Elevated Pressure, Ser. No.60/549,322, filed Mar. 1, 2004 and a Nonprovisional patent applicationentitled High-Pressure Power Cable Connector filed concurrentlyherewith, which are incorporated herein by reference in their entirety.

The actual permeation rate of a dielectric property-enhancing fluidthrough the insulation jacket is dependent on the fluid pressure in thecable interstices and rapid increases in dielectric performance can beimparted with higher, sustained pressures. To illustrate this benefitaccording to the present method, the following dielectricproperty-enhancing fluid mixtures were prepared: FLUID 1=25% (weight)acetophenone+75% (weight) p-tolylethylmethyldimethoxysilane; FLUID 2=25%(weight) acetophenone+75% (weight)vinylmethylbis(1-phenylethyleneoxy)silane (i.e., methylvinyl bis(1-phenyl ethenyloxy)silane). Using the novel high-pressure connectors,described above, each fluid mixture was injected into the interstitialvoid volume of a 220-foot coiled segment of 1/0, 175 mil XLPE cable at480 psig, and contained therein without leaking, according to thepresent method. This cable had been previously aged several years in anambient temperature water tank while a voltage of 2.5U₀ (i.e., 2.5×ratedvoltage) was applied thereto. The coils were immersed in a water bath ata controlled temperature of 25° C. After injection, but while the latentpressure was maintained on the coils by suitable injection devices andvalving, a voltage of 21.65 kV (i.e., 2.5×rated voltage) was applied.After 7 days, each cable was removed from the water bath and promptlycut into 6 samples for AC breakdown testing according to ICEAS-97-682-2000 10.1.3 “High Voltage Time Test Procedure,” wherein the keytest parameters were: 49-61 Hz, room temperature, 100 v/mil for 5minutes raised in 40 v/mil increments each 5 minutes to failure. Beforetreatment, a third identically aged sample was sacrificed to establishthe baseline performance for the laboratory aged cable. The results oftesting were plotted on Weibull graphs. The 63.3% probability breakdownvalue increased from 370 volts/mil for the aged cable to 822 volts/milfor the segment treated with FLUID 1 (i.e., a 2.22 fold or 122%improvement over the control). Similarly, the 63.3% probabilitybreakdown value increased from 370 volts/mil (control) to 999 volts/milfor the segment treated with FLUID 2 (i.e., a 2.7 fold or 170%improvement over the control). In each case, the 90% confidence boundsfor the Weibull curves were quite narrow at the 63.3% industryrecognized standard. These results stand in sharp contrast to a verysimilar experiment using the prior art approach (see above cited“Entergy Metro Case Study”) wherein CableCURE®/XL fluid was injectedinto a 25 kV, 750 kcmil cable at pressures of 30 and 117 psig.CableCURE/XL fluid is described in U.S. Pat. No. 5,372,841 and an MSDSsheet as a mixture of 70% phenylmethyldimethoxysilane (which has adiffusion coefficient of 5.73×10⁻⁸ cm²/sec at 50° C.) and 30%trimethylmethoxysilane (which has a diffusion coefficient of 2.4×10⁻⁷cm²/sec at 50° C.) and is thus analogous to the above fluid mixtureswith respect to the relative concentrations of rapidly diffusingcomponents and slower diffusing components as well as the absolutevalues of the diffusion coefficients of the former. In this study, thereported 63% breakdown value of the treated cables relative to controlincreased only 14.5% and 34.6% in seven days for the 30 psig and 117psig treated cables, respectively. It is thus seen that, in absoluteterms, the present method using the average performance of the aboverestorative fluid mixtures provides a (822+999)/2-370=541 volts/milimprovement. At best, this prior art employing a non-sustained pressuretreatment provided an improvement of 74.7 kV/262 mil−55.5kV/262=28−212=73 volts/mil, wherein 262 mils is the thickness of the 25kV cable's insulation. Put another way, the present method provides animprovement of at least about 640% over the old technology with respectto AC breakdown performance over a one week period.

In one embodiment of the method for enhancing the cable segment firstbeing discussed, the interstitial void volume of a cable segment isinjected (filled) with at least one dielectric property-enhancing fluid.As used herein with respect to the methods being discussed, a cablesegment is generally either a length of continuous electrical cableextending between two connectors used in the injection of one or moredielectric property-enhancing fluid into the length of cabletherebetween, or a length of electrical cable extending between two suchconnectors with one or more splice or other style connectorstherebetween operation in a flow-through mode. The actual pressure usedto fill the interstitial void volume is not critical provided theabove-defined elastic limit is not attained. After the desired amount ofthe fluid has been introduced, the fluid is confined within theinterstitial void volume at a sustained residual pressure greater than50 psig using the aforementioned two connectors defining the cablesegment, but below the elastic limit of the insulation jacket. It ispreferred that the residual pressure is between about 100 psig and about1000 psig, most preferably between about 300 psig and 600 psig. Further,for the method for enhancing the cable segment first being discussed, itis preferred that the injection pressure is at least as high as theresidual pressure to provide an efficient fill of the cable segment(e.g., 550 psig injection and 500 psig residual). In another embodimentthereof, the residual pressure is sufficient to expand the interstitialvoid volume along the entire length of the cable segment by at least 5%,again staying below the elastic limit of the polymeric insulationjacket. Optionally, the dielectric property-enhancing fluid may besupplied at a pressure greater than about 50 psig for more than about 2hours before being contained in the interstitial void volume.

In another embodiment, the method for enhancing the cable segment firstbeing discussed may be applied to a cable segment having a firstclosable high-pressure connector attached at one terminus thereof and asecond closable high-pressure connector attached at the other terminusthereof, each connector providing fluid communication with theinterstitial void volume of the segment. Each connector employs anappropriate valve to open or close an injection port, as furtherdescribed below. A typical sequence comprises initially opening bothvalves and introducing at least one dielectric property-enhancing fluidvia the port of the first connector so as to fill the interstitial voidvolume of the segment. At this point, the valve of the second connectoris closed and an additional quantity of the fluid is introduced via theport of the first connector under a pressure P greater than 50 psig.Finally, the valve of the first connector is closed so as to contain thefluid within the void volume at a residual pressure essentially equal toP.

Regardless of any particular embodiment, it is preferred that thedielectric property-enhancing fluid be selected such that the residualpressure decays to essentially zero psig in greater than 2 hours, butpreferably in more than 24 hours, and in most instances within about twoyears of containing the fluid, as discussed supra with respect to FIG.2. Furthermore, since the instant method can supply an additionalincrement of fluid to the interstitial void volume, it is alsocontemplated the method can be used to advantage to treat cable segmentswherein the weight of the dielectric property-enhancing fluidcorresponding to the interstitial void volume is less than the weight ofthe fluid required to saturate the conductor shield and the insulationjacket of the segment (i.e., a desirable amount for optimal treatment).Thus, the method for enhancing the cable segment first being discussedis particularly advantageous when applied to the treatment of round orconcentric stranded cables having a size of no greater than the abovementioned 4/0 (120 mm²), of compressed stranded cables having a size ofno greater than 250 kcm (225 mm²), and of compact stranded cables havinga size of no greater than 1000 kcm (500 mm²).

In view of the above mentioned pushback phenomenon, special connectorswhich are appropriately secured to the insulation jacket of the cableare preferably used to facilitate the instant method. Such connectors,as exemplified by the above described high-pressure terminal connectorof FIG. 3 and further described below, employ either external orintegral valves which allow fluid to be introduced into the cablesegment as well as confined at the residual high pressure. Such a valvecan also serve to withdraw water and/or contaminated fluid from theother, remote end of the cable segment. For example, in the connectorshown in FIG. 3, at least one injection port is fitted with an externalquick-disconnect coupling such that, after injection, the pressurizedfluid supply can be readily disconnected and the injected fluid trappedwithin the connector housing and the interstitial volume of the cable ata residual pressure P throughout the entire length of the cable segmentbeing treated. It is preferred that miniaturized versions ofconventional quick-disconnect couplings are used and that these fitessentially flush with the outer surface of the housing to provide aprotrusion-free or low profile outer surface for the high-pressuresplice connector to readily receive subsequent insulation component(s)and avoid any sharp electrical stress concentration points. Otherpreferred high-pressure connectors which may advantageously be utilizedin the practice of the present method are described below with referenceto the drawings illustrating exemplary embodiments thereof, wherein thesame reference numerals are applied to identical or correspondingelements.

A swagable high-pressure terminal connector 81 which may be used in theinstant method is shown in FIG. 5. The housing 80, having internalmachined teeth 32, is sized so that its ID (inner diameter) is justslightly larger than the OD (outer diameter) of insulation jacket 12 andis configured to receive the end portion of cable segment 10 therein.Housing 80 is integral with a termination crimp connector portion 82. Inapplication, the termination crimp connector portion 82 is crimped toconductor 14 of cable 10 at an overlapping region to secure it theretoand provide electrical communication therewith. Housing 80, furthercomprises a self closing spring-actuated valve 36 (illustrated inenlarged detail in FIG. 6) disposed at injection port 48 forintroduction of the dielectric property-enhancing fluid. After housing80 is placed in the position shown in FIG. 5, a swage is applied to theperiphery of housing 80 over circumferential teeth 32 such that teeth 32deform and partially penetrate insulation jacket 12 along a peripherythereof sufficiently so as to simultaneously form a fluid-tight sealagainst the insulation jacket and prevent pushback (as described above)of the insulation jacket when the cable segment is subjected tosustained interior pressure.

As used herein, swaging or “circumferential crimping” refers to theapplication of radial, inwardly directed compression around theperiphery of the housing over at least one selected axial positionthereof. This swaging operation produces a circular peripheral indentedregion (e.g., a groove or flat depression) on the outer surface of thehousing and inwardly projects a corresponding internal surface thereofinto the insulation jacket (or bushing or splice crimp connector) so asto partially deform the latter at a periphery thereof. Swaging can beaccomplished by methods known in the art, such as a commerciallyavailable CableLok™ radial swaging tool offered by Deutsch MetalComponents, Gardena, Calif. Swaging is to be distinguished from a normalcrimping operation, wherein one-point (indent crimp), two-point ormulti-point radial crimps are applied to join crimp connectors usingtools well known in the art (e.g., the crimp connectors attached to theconductor). The resulting crimp from such a single or multi-pointcrimping operation is referred to simply as “crimp” herein and may beaccomplished with shear bolts.

The injection valve 36 used in the above high-pressure swagable terminalconnector (FIG. 5) is an example of an integral valve and is illustratedin detail in FIG. 6. A hollow injection needle 42 having side port(s) 46and injection channel 44 is shown in position just prior to injecting apressurized fluid. Needle 42 includes a concave portion at its tip whichmates with a corresponding convex profile 90 on plug-pin 86, the latterbeing attached to C-shaped spring 34, which rides on a peripheral innersurface of housing 80 and preferably within a slightly indented channelin the latter. This mating with the needle tip assures that a plug-pin86 carried by the C-shaped spring 34 is centered in, and just displacedfrom, injection port 48 while needle 42 is inserted and likewise centersthe plug-pin 86 in the injection port 48 of housing 80 as the needle 42is withdrawn. The convex and concave surfaces could, of course, bereversed and other shapes could be utilized to achieve the same effect.The plug-pin 86 and an O-ring 88 with the plug-pin to extendingtherethrough, in combination provide a fluid-tight seal when the needletip is withdrawn and C-shaped spring 34 presses against O-ring 88 so asto deform the latter into a slight saddle shape, whereby the O-ring 88seats against the inside surface of the housing 80 and the outsidesurface of C-shaped spring 34. It will be appreciated that, as thepressure within the housing 80 increases, the compressive force on theO-ring 88 increases and thereby improves the sealing performance ofO-ring 88. In practice, a clamp assembly (not shown) which houses needle42 is mounted over injection port 48 to form a fluid-tight seal to theexterior of housing 80. As the tip of needle 42 is actuated and insertedinto injection port 48, thereby depressing plug-pin 86 and unseatingO-ring 88, fluid can be injected into or withdrawn from the interior ofhousing 80 through needle 42.

A preferred dual-housing, swagable high-pressure splice connector 101,which can be assembled from two identical swagable high-pressureterminal connectors, is illustrated in FIG. 7. In a typical assemblyprocedure using this embodiment, described here for one of the two cablesegments 10 shown in FIG. 7, the insulation jacket 12 is first preparedfor accepting a splice crimp connector 18, as described above. A housing100, which includes injection port 48, is sized such that its larger IDat one end portion is just slightly larger than the OD of insulationjacket 12 and its smaller ID at an opposite end portion is just slightlylarger than the OD of splice crimp connector 18. The housing 100 is slidover the corresponding conductor 14 and insulation jacket 12, and thesplice crimp connector 18 is then slipped over the end of the conductor14 and within the housing. Preferably, the lay of the outermost strandsof conductor 14 of the cable segment 10 is straightened to anorientation essentially parallel to the axis of the cable segment 10 tofacilitate fluid flow into and out of the respective interstitialvolume, as well known in the art. Housing 100, having O-ring 104residing in a groove therein, is swaged with respect to splice crimpconnector 18. The swage is applied at position 102 over the O-ring 104and the machined teeth 108, which may have a profile varying fromroughly triangular to roughly square. This swaging operation joins theconductor 14, splice crimp connector 18, and housing 100 in intimatemechanical, thermal and electrical contact and union, and provides aredundant seal to the O-ring 104. Swaging can be performed in a singleoperation, as described above, or in phases (i.e. wherein splice crimpconnector 18 is first swaged together with conductor 14, and thenhousing 100 is swaged with the splice crimp connector/conductorcombination 18/14, provided that the length of the splice crimpconnector and length of the housing can accommodate sliding housing 100out of the way or in the unusual event that the splice crimp connectorOD is greater than the insulation OD (e.g., as sometimes found inJapan). In either event, this swaging assures intimate mechanical,thermal and electrical contact and union between housing 100, splicecrimp connector 18 and conductor 14; it also results in a fluid-tightseal between housing 100 and splice crimp connector 18. When the spliceaccording to this embodiment is to be used in a flow-through mode, waterstop region 106 (i.e., a barrier wall within splice crimp connector 18)may be omitted or drilled out prior to assembly. To facilitate flowthrough the swaged conductor area, at least one micro tube (not shown)of sufficiently high strength to avoid crushing during subsequentswaging and of sufficient length to allow fluid communication betweenthe annular spaces remaining at each end of the crimp connector 18, maybe placed within the annulus formed between the two conductors 14 andthe crimp connector 18 when the water stop region 106 is omitted. Aswage is then applied to the exterior of housing 100 over machined teeth32 such that teeth 32 deform insulation jacket 12 sufficiently to form afluid tight seal and prevent pushback of the insulation jacket when thecable segments are pressurized. The injection port 48 on housing 100allows fluid to be injected or withdrawn at elevated pressures employinga valve 36 of the type described in FIG. 6 above. When the swagablehigh-pressure splice connector according to this embodiment is to beused in a flow-through mode, the injection ports may be omitted.

The above high-pressure connectors allow two cable segments to beinjected simultaneously using appropriate fitting(s) and injectionport(s). Alternatively, two (or more) segments can be injectedsequentially starting at an end of the first segment distal to thehigh-pressure splice connector, through the high-pressure spliceconnector and then through the second segment (flow-through mode). Inthis, and any other so-called flow-through mode, the injection port(s)may be eliminated.

In general, the components of the high-pressure connectors, except forany rubber (elastomeric) washers or rubber O-rings employed, aredesigned to withstand the anticipated pressures and temperatures and maybe fabricated from a metal such as aluminum, aluminum alloy, copper,beryllium-copper, or stainless steel. It is also possible to employnon-conductive components if the high-pressure terminal or spliceconnector design accommodates electrical communication between theassociated termination crimp connector or splice crimp connector (i.e.,with the conductor in each case) and any subsequently applied conductiveinsert. That is, the semi-conductor portion of any termination or splicebody applied over the high-pressure terminal connector or spliceconnector, as conventionally practiced in the art, should be essentiallyat the same electrical potential as the conductor. Preferably, thickaluminum or copper washers, in conjunction with rubber washers are usedin connectors employing compression seals, as illustrated in FIG. 3.Since these metals exhibit high thermal conductivities, they facilitatedissipation of heat in the load-carrying termination or splice, therebyreducing the temperature at the surface of the insulation jacketproximal to the respective connector. Rubber washers and O-rings may beformed from any suitable elastomer compatible with the fluid(s)contemplated for injection as well as the maximum operating temperatureof the connector. Preferred rubbers include fluorocarbon rubbers,ethylene-propylene rubbers, urethane rubbers and chlorinatedpolyolefins, the ultimate selection being a function of the solubilityof, and chemical compatibility with, the fluid(s) used so as to minimizeswell or degradation of any rubber component present. It is contemplatedthat any high-pressure splice or dead-front terminal connector providesfor electrical contact between the respective splice crimp connector ordead-front termination crimp connector and the corresponding conductiveinsert, as commonly practiced in the art, in order to prevent electricaldischarges or corona. In addition, it is preferred that there be goodthermal contact between the conductor and the housing (e.g., using setscrews, crimping) to provide for heat dissipation away from theconductor.

As will be apparent to those skilled in the art, a high-pressure spliceconnector is generally symmetrical with respect to a plane perpendicularto the cable axis and through the center of the splice crimp connector,and the assembly procedures described are applied to both ends of thesplice. It also will be recognized that different combinations ofsealing and securing options, such as illustrated herein, may becombined in “mix-and-match” fashion to provide the intended sealing andsecuring functions, although the skilled artisan will readily determinethe more desirable and/or logical combinations.

In general, the dielectric property-enhancing fluid used (also referredto a tree retardant agent or anti-treeing agent herein) may be selectedfrom any of the compounds known in the art to prevent water trees inpolymeric insulation when compounded into the insulation material and/orinjected into a new or an in-service cable. Such compounds as aromaticketones (e.g., acetophenone), fatty alcohols (e.g., dodecanol), UVstabilizers (e.g., 2-ethylhexyltrans-4-methoxycinnamate), andorganoalkoxysilanes, illustrate the range of compounds which can beemployed as the dielectric-enhancing fluid in the present method. Manysuch compounds have been described in the patent literature and theinterested reader is referred to U.S. Pat. No. 4,144,202 to Ashcraft etal., U.S. Pat. No. 4,212,756 to Ashcraft et al., U.S. Pat. No. 4,299,713to Maringet et al., U.S. Pat. No. 4,332,957 to Braus et al., U.S. Pat.No. 4,400,429 to Barlow et al., U.S. Pat. No. 4,608,306 to Vincent, U.S.Pat. No. 4,840,983 to Vincent, U.S. Pat. No. 4,766,011 to Vincent et al,U.S. Pat. No. 4,870,121 to Bamji et al., U.S. Pat. No. 6,697,712 toBertini et al. and U.S. Pat. No. 5,372,841 to Kleyer et al., amongothers.

According to the method for selecting formulations to treat electricalcables to be more specifically discussed below, it is contemplated thatthe dielectric property-enhancing fluid may be a mixture of two or morefluids of the type describe herein, provided that such a mixture remainsfluid under the conditions of the actual injection. Specific,non-limiting, examples of suitable dielectric property-enhancingmaterials may be selected from one or more of the following:

-   phenylmethyldimethoxysilane-   phenyltrimethoxysilane-   diphenyldimethoxysilane-   phenylmethyldiethoxysilane-   trimethylmethoxysilane-   acetonitrile-   benzonitrile-   tolyinitrile-   t-butyldiphenylcyanosilane-   1,3-bis(3-aminopropyl)tetramethyldisiloxane-   1,4-bis(3-aminopropyldimethylsilyl)benzene-   3-aminopropylpentamethyldisiloxane-   aminomethyltrimethylsilane-   1,4-bis(3-aminopropyldimethylsilyl)benzene-   3-aminopropylmethylbis(trimethylsiloxy)silane-   (4-bromophenylethynyl)trimethylsilane-   p-chlorophenyltrimethylsilane-   bis(cyanopropyl)tetramethyldisiloxane-   4-aminobutyltriethoxysilane-   bis(3-cyanopropyl)dimethoxysilane-   N-methylaminopropylmethyldimethoxysilane-   N-(3-methacryloxy-2-hydroxypropyl)-3-aminopropyltriethoxysilane-   N-ethylaminoisobutyltrimethoxysilane-   3-(2,4-dinitrophenylamino)propyltriethoxysilane-   N,N-dimethylaminopropyl)trimethoxysilane-   (N,N-diethyl-3-aminopropyl)trimethoxysilane-   N-butylaminopropyltrimethoxysilane-   bis(2-hydroxyethyl)-3-aminopropyltriethoxysilane-   3-aminopropyltris(methoxyethoxyethoxy)silane-   3-aminopropyltrimethoxysilane-   3-aminopropylmethyldiethoxysilane-   3-aminopropyldimethylethoxysilane-   p-aminophenyltrimethoxysilane-   m-aminophenyltrimethoxysilane-   3-(m-aminophenoxy)propyltrimethoxysilane-   aminomethyltrimethylsilane-   N-(2-aminoethyl)-11-aminoundecyltrimethoxysilane-   N-(6-aminohexyl)aminopropyltrimethoxysilane-   N-(2-aminoethyl)-3-aminopropyltrimethoxysilane-   N-(2-aminoethyl)-3-aminopropylmethyldimethoxysilane-   N-(2-aminoethyl)-3-aminoisobutylmethyldimethoxysilane-   3-(N-allylamino)propyltrimethoxysilane-   11-cyanoundecyltrimethoxysilane-   2-cyanoethyltrimethoxysilane-   2-cyanoethyltriethoxysilane-   2-cyanoethylmethyldimethoxysilane-   (3-cyanobutyl)methyldichlorosilane-   bis(3-cyanopropyl)dimethoxysilane-   3-(triethoxysilylpropyl)-p-nitrobenzamide-   2-(diphenylphosphino)ethyltriethoxysilane-   3-cyanopropylphenyldimethoxysilane-   bis(3-cyanopropyl)dimethoxysilane-   phenyltris(methylethylketoximio)silane-   vinylmethylbis(methylethylketoximino)silane-   vinyltris(methylethylketoximino)silane-   phenylmethylbis(dimethylamino)silane-   phenethyldimethyl(dimethylamino)silane-   n-octyldiisopropyl(dimethylamino)silane-   n-octadecyldimethyl(dimethylamino)silane-   bis(dimethylamino)vinylmethylsilane-   bis(dimethylamino)vinylethylsilane-   bis(dimethylamino)diphenylsilane-   vinyltris(methylethylketoximino)silane-   vinylmethylbis(methylethylketoximino)silane-   phenyltris(methylethylketoximio)silane-   phenyloctyidialkoxysilane-   dodecylmethyldialkoxysilane-   n-octadecyldimethylmethoxysilane-   n-decyltriethoxysilane-   dodecylmethyldiethoxysilane-   dodecyltriethoxysilane-   hexadecyltrimethoxysilane-   1,7-octadienyltriethoxysilane-   7-octenyltrimethoxysilane-   2-(3-cyclohexenyl)ethyl]trimethoxysilane-   (3-cyclopentadienylpropyl)triethoxysilane-   21-docosenyltriethoxysilane-   (p-tolylethyl)methyldimethoxysilane-   4-methylphenethylmethyldimethoxysilane-   divinyldimethoxysilane-   o-methyl(phenylethyl)trimethoxysilane-   styrylethyltrimethoxysilane-   (chloro p-tolyl)trimethoxysilane-   p-(methylphenethyl)methyldimethoxysilane-   2-hydroxy-4-(3-triethoxysilylpropoxy)diphenylketone-   dimesityldimethoxysilane-   di(p-tolyl))dimethoxysilane-   (p-chloromethyl)phenyltrimethoxysilane-   chlorophenylmethyldimethoxysilane-   SF₆ (sulfur hexafluoride)-   fluorocarbons or halocarbons-   chlorophenyltriethoxysilane-   phenethyltrimethoxysilane-   phenethylmethyldimethoxysilane-   N-phenylaminopropyltrimethoxysilane-   (aminoethylaminomethyl)phenethyltriethoxysilane-   3-cyanopropylmethyldimethoxysilane-   methylphenyl bis (1-phenyl ethenyloxy)silane-   methylvinyl bis (1-phenyl ethenyloxy)silane

Thus, for example, the fluid may be a mixture of the type disclosed inU.S. Pat. No. 5,372,841 comprising (A) at least one antitreeing agent;and (B) a water-reactive compound, the water-reactive compound having adiffusion coefficient of greater than 10⁻⁷ cm²/second at 50° C. in thepolymeric insulation and the mixture having an initial viscosity of ≦100cP at 25° C., and wherein (A) and (B) are different. A particular fluidof this type is a mixture an aryl-functional alkoxysilane, such asphenylmethyldimethoxysilane or phenyltrimethoxysilane, and awater-reactive compound selected from trimethylmethoxysilane ordimethyldimethoxysilane.

A preferred dielectric property-enhancing fluid is a mixture containingat least one component having a permeability of less than 10⁻¹⁰g/second-cm at 25° C. in the insulation polymer and containing no morethan two water-reactive groups in each molecule. The above component hasa dielectric constant which is at least twice that of the polymericinsulation. An example of such a component is a cyanoalkoxysilane whichcan have the formulaR_(x)R′_(y)Si(OR″)_(z)wherein x=1 or 2, y=0 or 1, z=1, 2 or 3, and x+y+z=4, and wherein R is acyano-containing organic group having 3-13 carbon atoms, R′ is anorganic group having 1 to 3 carbon atoms, preferably a hydrocarbongroup, and OR″ is a water-reactive group selected from an alkoxy grouphaving 1 to 3 carbon atoms or an enol ether group. Preferably x=1, y=1,z=2, R is selected from isomers of cyanobutyl, cyanopropyl or cyanoethylgroups, R′ is methyl, and OR″ is a methoxy group. Specificcyano-containing alkoxysilanes include cyanoethylmethyldimethoxysilane,cyanopropylmethyldimethoxysilane and cyanobutylmethyldimethoxysilane,inter alia.

It is also preferred that the dielectric property-enhancing fluid is amixture of acetophenone with one or more of the above materials,preferably containing less than about 30% (weight) of the latter. Suchcompositions containing acetophenone preferably also include at leastone material selected from methylphenyl bis (1-phenyl ethenyloxy)silane,methylvinyl bis (1-phenylethyleneoxy)silane,p-tolylethylmethyldimethoxysilane, cyanobutylmethyldimethoxysilane, andcyanopropylmethyldimethoxysilane.

The unexpected increase in injection volume possible with the method forenhancing the cable segment first being discussed (i.e., the abovementioned permeation-adsorption gap) offers advantages beyond theaforementioned elimination of the soak phase utilized by the purveyorsof the prior art. For example, the present method allows levels ofactive ingredients to be supplied to the cable beyond the equilibriumsaturation values suggested by the prior art. This extra dielectricproperty-enhancing fluid provides further flexibility in tailoringtreatment fluid combinations which target short-term reactiveperformance as well as preemptive performance (i.e., a preventivetreatment for long-term performance). In each of these cases, theadvantages of reactive and preemptive performance can be realizedwithout the need to compromise the proactive performance (i.e.,treatment for medium term when cable is statistically likely to fail innear future) targeted by the prior art approach. Moreover, the totalamount of such a fluid mixture introduced can be easily adjusted byselecting the injection and residual pressures, according to the methodfor enhancing the cable segment first being discussed, to tailor theinjection to the cable owner's economic or technical requirements. Thus,while it is likely that the short-term performance of any treatmentfluid will benefit from the higher transport rates described herein, themethod also allows the introduction of an entirely new class ofmaterials which, without the benefit of the current method, would notdiffuse appreciably into the insulation or could not be efficientlysupplied in sufficient volume to the interstitial void volume. Such acomponent, defined herein as a Class S material has a permeability ofless than about 10⁻¹⁰ g/second-cm at 25° C. as well as solubility ofabout 0.0001 to about 0.02 gram/cm³ at 25° C. or has a diffusivity(diffusion coefficient) of less than about 10⁻⁸ cm²/sec at 50° C., eachproperty being determined in the insulation polymer. The method allowsthe use of Class S materials since it accelerates permeation of fluidinto the insulation while the pressure is still high enough to providean enhanced driving force and it addresses the above mentionedobservation that many in-service cables present an inadequateinterstitial void volume relative to the volume of fluid required totreat the cable. The inclusion of such a slowly diffusing material inthe fluid composition being injected is believed to impart improvedlong-term (e.g., 10 to 40 years) performance. If such a Class S materialwere used in the methods of the prior art, a corresponding reduction inthe amount of short-term performance materials, medium-term performancematerials, or both, would have to be made. In the former case it isunlikely that the inadequately treated cable would provide reliableperformance for the time required to recognize any benefits from the lowdiffusivity materials. In the alternative, the costly and dangerous soakphase would have to be greatly extended, this option being effectivelyprohibited by the safety and economic implications.

It is therefore preferred that at least two classes of materials, andmore preferably three classes, are combined to provide the dielectricproperty-enhancing fluid. Optimum amounts and optimum ratios of suchcomponents are selected based on the specific geometry of the cablebeing treated and the performance characteristics desired by the circuitowner. These three classes are defined as follows, wherein each propertyis measured in the cable insulation material at the indicatedtemperature:

-   -   Class Q—Quickly diffusing materials having a diffusion        coefficient greater than about 10⁻⁷ cm²/sec at 50° C., such as        acetophenone and trimethylmethoxysilane or other high        diffusivity materials disclosed in the above cited U.S. Pat. No.        5,372,841. Such materials impart short-term performance        (reactive performance) (generally, 0 to about 12 months).    -   Class M—Moderately diffusing materials having a diffusion        coefficient greater than about 10⁻⁸ cm²/sec, but less than about        10⁻⁷ cm²/sec at 50° C., such as phenylmethyldimethoxysilane and        p-tolylethylmethyldimethoxysilane. Such materials impart        medium-term performance (proactive performance) (generally about        12 to about 120 months).    -   Class S—Slowly diffusing materials or low solubility materials,        as discussed above, having a low solubility of about 0.0001 to        about 0.02 gram/cm³ at 25° C. or having a diffusivity less than        about 10⁻⁸ cm²/sec at 50° C., and having a permeability less        than about 10⁻¹⁰ g/cm·s at 25° C., each property being measured        in the insulation material, such as        cyanobutylmethyldimethoxysilane, cyanoethylmethyldimethoxysilane        and cyanopropylmethyldimethoxysilane. Such materials impart        long-term (preemptive) performance (generally greater than about        120 months).

For each desired class of material to be employed, the optimumconcentration in the strand shield (conductor shield) and the insulationjacket are calculated or determined by experiment. For materials withsolubility greater than about 0.02 grams/cm³ at 25° C. (many Class Q andCass M materials fall into this category), this optimum is generally therespective saturation level at average soil temperature at the depth thecable is buried, often at about 1 meter. Supply of fluid substantiallyabove this level has been shown to result in the above describedsuper-saturation which may be deleterious to the circuit reliability. Inview of the low solubility of Class S materials, their optimumconcentration is generally greater than the saturation level since thereis little chance of damage due to this phenomenon, and the effectivelife of the treated cable increases with the amount of Class S materialsupplied.

It is believed that materials of one of the above defined classesinteract little with materials from another class since thediffusivities between any two classes typically differ by an order ofmagnitude. Furthermore, it has been well established in the art that thesolubility of oligomers is substantially less than that of correspondingmonomers. Therefore, damage to a cable due to supersaturation over longperiods of time using constituents which form oligomers (e.g.,organoalkoxysilane reacting with adventitious water in the cable) is nota concern. Thus, to enjoy the benefits of short-term, medium-term, andlong-term reliability performance, the present method teaches thefollowing protocol:

-   -   (a) The saturation (or other optimum level) for each material        class (i.e., there may be two or more components within each        material class) is measured (or calculated) in the conductor        shield and insulation. The optimum level (or the minimum optimum        level for low solubility components) should preferably account        for the anticipated average conductor shield and insulation        temperature and the typical temperature cycling (ΔT) over the        anticipated lifetime of the cable.    -   (b) The concentration of each class and each component in the        conductor shield, as determined in step (a), is multiplied by        the specific mass of the conductor shield to give the required        weight of the respective class and component therein. Likewise,        the concentration of each class and each component in the        insulation jacket, is multiplied by the specific mass of the        insulation to give the required weight of the respective class        and component therein, each such calculation being appropriately        adjusted to reflect the actual cable segment length. These        products are then summed to provide the total minimum weight of        fluid mixture required to treat the segment.    -   (c) A starting pressure in excess of 50 psig is assumed and the        minimum weight of fluid required from step (b) is compared to        the total weight corresponding to total volume available (i.e.,        interstitial+annular+adsorption/permeation gap) at this        pressure. The interstitial void volume can be easily calculated        from the strand conductor geometry, as described in U.S. Pat.        No. 5,279,147. The annular volume for a given cable, as a        function of the pressure, can be obtained from rigorous        calculations, as described above which provide a plot similar to        FIG. 1, lower curve. The adsorption/permeation gap volume can        also be obtained from a plot similar to FIG. 1 (upper curve for        a given mix of components and for a given cable). Alternatively,        once the previously discussed adsorption/permeation gap is        experimentally determined as a function of pressure for a given        mix of components and a first cable geometry, this data can be        used to provide a good approximation of the corresponding gap        values for a second cable by multiplying the former data by the        ratio of the cross-sectional area of the second conductor shield        to that of the first cable.    -   (d) If there is sufficient total volume (weight) available        (which may be the case for some cables with larger and less        compacted conductors), the amount of Class S material (or a low        solubility Class Q or Class M material) is increased until the        total volume supplied equals the available total volume.    -   (e) If there is not sufficient total volume available at the        minimum pressure, the pressure is increased and step (c) is        iterated until at least the minimum total volume (weight) of        fluid can be accommodated.

Based on the above protocol, the candidate composition is mixed prior toinjection and the prescribed amount thereof is injected into theinterstitial void volume of the cable segment at the appropriatepressure using one of the herein described high-pressure connectors.Once the prescribed quantity of fluid is delivered, the injection isterminated and the fluid confined within the interstitial void volume ata similar residual pressure. Thus another embodiment of the method forenhancing the cable segment first being discussed comprises filling theinterstitial void volume of a cable segment with the amount of thedielectric property-enhancing fluid composition required to saturate theconductor shield and the insulation jacket of the cable segment (W_(s))at a pressure P, and confining it therein at a similar residualpressure, as previously described. In this embodiment, when W_(s) isgreater than the weight (W_(i)) of this composition which can beinjected into the interstitial void volume at pressure P, the pressureis adjusted according to the above protocol such that W_(s)=W_(i). Onthe other hand, when W_(s) is less than W_(i), an additional weight (W)of at least one Class S material is added to the composition beforeinjecting the composition such that (W+Ws)=W_(i).

To further clarify the above protocol, two examples of its applicationare provided. These examples employ hypothetical formulations, areprovided for illustrative purposes only and do not represent actualdata. They are not to be construed as limiting the scope of the anymethod discussed herein.

Example 1 illustrates the determination of the optimum treatment for1000 feet of concentric I/O, 100% XLPE insulation cable. A preliminaryformulation, shown in the table below, which provides the desiredreliability benefits, is selected. The treatment fluid comprisesacetophenone (a Class Q material),vinylmethylbis(1-phenylethyleneoxy)silane (VMB, a Class M material) andS1 and S2 (two typical Class S materials). The concentrations (weightpercent=100×solubility in g/cm³, where the insulation is XLPE with adensity of about 1 g/cm³) have been arbitrarily selected for optimumperformance, either from empirical observations, theoreticalconsiderations such as saturation levels, or both. The specific gravityof the fluid mixture is 1.03. Acetophenone VMB S1 S2 Weight % solute1.0% 3.5% 0.5% 0.5% in insulation jacket Weight % solute 3.0% 16.0% 1.0%1.0% In conductor shield

The cross-sectional areas for the insulation jacket (A_(in)) and theconductor shield (A_(cs)), are each calculated from simple geometricprinciples, as discussed above. These are used to calculate therespective specific volumes (expressed in ft³/kft) in the insulation andconductor shield, respectively, as shown in the following table.Specific volume of insulation (Vi) 2.34 =A_(in) · 1000 ft · 1² ft²/12²in² Specific volume of conductor 0.289 =A_(cs) · 1000 ft · 1² ft²/12²in² shield (V_(cs))

Each specific volume is then multiplied by each selected componentconcentration from the previous table. These results are illustratedbelow, wherein the total calculated fluid requirement to treat the 1000ft segment is about 12.2 pounds and the fractions of each of its fourcomponents are also displayed (e.g., for the VMB fluid in the conductorshield: 0.289 (ft³/kft)×62.4 lb/ft³×1.03 (density)×0.16 (% of VMB)=2.97lb). Wt. of Aceto- Mixture phenone VMB S1 S2 Specific component mass in8.26 1.50 5.26 0.75 0.75 insulation Specific component mass in 3.91 0.562.97 0.19 0.19 conductor shield Total Component Mass 12.17 2.06 8.230.94 0.94

A minimum injection pressure of 300 psig is arbitrarily chosen toprovide a rapid increase in post-injection dielectric performance andthe respective amounts of fluid (expressed in pounds for the 1000 ftsegment) which can be accommodated are calculated or obtained from aplot similar to FIG. 1, according to the above discussed protocol. Theseare displayed in the table below, wherein A_(i)=cross-sectional area ofinterstices; A_(a)=cross-sectional annular area at 300 psig; SG=specificgravity of fluid mix. Specific mass within interstices 5.4 A_(i) · SG ·1000 · 62.4/12² Specific mass within annulus 3.00 A_(a) · SG · 1000 ·62.4/12² Specific mass-adsorption/permeation 2.39 From appropriate graphTotal Specific Mass Supplied 10.8

It is seen that the amount of fluid supplied at 300 psig is only 10.8pounds, this being 1.4 pounds (i.e., 12.2-10.8) short of the previouslydetermined optimum amount. The present method teaches an increase inpressure until the optimum quantity of fluid (i.e., 12.2 lb) can besupplied to the cable segment. For this example, the results of theiterative calculation according to the above described protocol whereinthe pressure is increased to 359 psig are displayed in the table below,wherein A_(a)′=annular cross-sectional area at 359 psig. Specific masswithin interstices 5.4 A_(i)′ · SG · 1000 · 62.4/12² Specific masswithin annulus 3.61 A_(a) · SG · 1000 · 62.4/12² Specificmass-adsorption/permeation 3.14 From appropriate graph Total SpecificMass Supplied 12.2

Example 2 illustrates the above protocol applied to the optimumtreatment of a 1000 ft concentric 750 kcmil, 100% XLPE insulation, cablesegment. The fluid formulation of Example 1 is again assumed and thevarious calculations shown therein are made using the correspondingdimensions of this cable's geometry. Specific volume of insulation(ft³/kft) 4.84 Specific volume of conductor shield (ft³/kft) 1.10

Again, each specific volume in the table above is multiplied by eachdesired concentration component in the formulation table (see Example1). These results are illustrated below, wherein the total fluidrequirement to treat 1000 feet of cable is 32.0 pounds and therespective fractions of its four components are displayed. Aceto-Mixture phenone VMB S1 S2 Specific component mass in 17.1 lb 3.11 10.891.55 1.55 insulation Specific component mass in 14.9 lb 2.12 11.31 0.710.71 conductor shield Total Component Mass 32.0 lb 5.22 22.16 2.26 2.26

A minimum injection pressure of 100 psig is chosen to provide a rapidincrease in post-injection dielectric performance. The interstitial,annular and adsorption/permeation gap volumes are calculated or obtainedfrom a plot similar to FIG. 1, according to the above describedprotocol, and converted to the corresponding amount of the respectivecomponents, as shown in the following table. The specific mass suppliedat 100 psig is about 66.8 pounds, or more than twice the minimum optimumrequirement. Specific mass within interstices 54.2 lb =A_(i) · SG · 1000· 62.4/12² Specific mass within annulus 11.1 lb =A_(a) · SG · 1000 ·62.4/12² Specific mass-adsorption/  1.5 lb From appropriate graphpermeation Total Specific Mass Supplied 66.8 lb

Rather than wasting the excess volume with a diluent as taught by U.S.Pat. No. 6,162,491, the present method teaches an increase in the supplyof Class S materials which provide further extension to the treatedcable's reliable life. That increase in the Class S materials to supplya total of the 66.8 lb of fluid, as previous shown to be accommodated bythis segment, is demonstrated by revision of the fluid formulation, asshown in the table below. Aceto- Mixture phenone VMB S1 S2 Specificcomponent mass in 17.1 lb 3.11 10.9 1.55 1.55 insulation Specificcomponent mass in 14.8 lb 2.12 11.3 0.71 0.71 conductor shield Class Smaterials above 34.9 lb 17.45 17.45 minimum Total 66.8 lb 5.23 22.2 19.719.7

A further advantage of the method for enhancing the cable segment firstbeing discussed is the elimination of the costly and dangerous step ofevacuating a cable prior to, and during, fluid injection. The method ofthe prior art is costly, primarily because of the labor involved. Aninjection team must wait for complete evacuation of the cable beforeinjection is commenced. The prior art method can create a potentiallydangerous condition when applied to energized cables in view Paschen'sLaw, which predicts a decrease in dielectric strength of air (or othergas) at reduced pressures. Application of a vacuum in the prior artmethod is preferred and currently practiced since this facilitates acomplete fill. In the absence of a vacuum, bubbles would likely form asthe fluid flowed through termination cavities or splice cavities or eventhrough the tangle of interstices of the cable strands. Even when higherpressures are utilized, the pressure is always released once theinjection is complete, and any gas bubbles which were temporarilydissolved in the fluid at the elevated pressure will immediatelyeffervesce, resulting in a portion of the cable being untreated or undertreated. Further, the vacuum is desirable in the prior art method sincea typical −13 psig pressure provides a 45% or greater driving force toaccelerate the flow of fluid down the length of cable, and indeedimproves the likelihood that the fluid will flow through the entirelength of the cable and therefore avoid a failed injection. The methodfor enhancing the cable segment suffers none of these problems. First,at the preferred pressures contemplated herein, the flow rate of thefluid is much higher and is much more likely to scour water orcontaminants with its greater shear. Further it is believed that even ifa small gas bubble is present, it will quickly dissolve in the fluidunder the influence of the residual pressure and will not immediatelyeffervesce to create a new bubble. Instead, the gas will now diffuseaxially in the fluid to distribute itself at a very low concentration,but still at a relatively high partial pressure. Because of the highpartial pressure the gas will quickly diffuse out of the cable into thesurrounding soil. Thus the method avoids the use of such a costly anddangerous vacuum.

Another advantage of the method for enhancing the cable segment firstbeing discussed is that there is no need to desiccate the strands of thecable segment. Because of the high flow and higher sheer forcesdescribed earlier, most of the water, or other contaminants in a cable,will be flushed from the interstices by the injection. Even if somewater is left in the strands, the method is less sensitive to the water,because an excess of water reactive fluid can be supplied.

Because the prior art method injects fluid through splices which werepreviously installed, there is a need to test each splice's ability toaccommodate flow and pressure. Yet another advantage of the method forenhancing the cable segment first being discussed, when combined withthe novel connectors described above, is that there is now no need toflow test and pressure test the strands of a medium voltage power cable.Again, because of the high injection pressures preferably used herein itis believed that almost all stranded cables will flow. Leak testing isobviated since the connectors employ devices designed to accommodate thehigher pressures.

The method for selecting formulations to treat electrical cables of thepresent invention by injection into a cable segment utilizes a method ofmatching the needs of the cable and the cable owner with a portfolio ofmaterials, each of which addresses different sets of technical,operational and economic issues. A unique cocktail is mixed with eithercircuit-owner cable size granularity, or even individual cablegranularity, in order to meet the requirements of the circuit owner. Inother words performance is optimized for each application based on amenu of end-user choices, geometry, cable operational history, andforecasted operational loads instead of the one-size-fits-all approachused in the prior art. A partial list of properties and commercialelements which may be controlled and optimized to establish a targetformulation includes the following:

Five Ps of Performance

-   -   (1) Post-failure or short-term performance (<12 months);    -   (2) Proactive or medium-term performance (12 months to 10        years);    -   (3) Preemptive or long-term performance (>10 years);    -   (4) Price (including fluid costs, process labor intensity, and        duration & scope of warranty);    -   (5) Properties (including compatibility with aluminum or copper        conductors and flammability);        Three Parameters    -   (6) Cable geometry;    -   (7) Anticipated cable temperature profile (typical) which        depends upon . . .        -   a. average load,        -   b. ground temperature at cable depth,        -   c. soil thermal conductivity;    -   (8) ΔT (anticipated temperature cycling; typical)        -   a. maximum load,        -   b. minimum load,        -   c. soil thermal conductivity.

In the present method for selecting formulations at least one class offluids, more preferably two classes of fluids and even more preferablythree classes of fluids are supplied in optimum amounts. Two or moreclasses are used in optimum ratios depending on the specific geometry ofthe cable being treated and the performance characteristics desired bythe circuit owner. As described above, the three classes of materialsare:

-   Class Q—Quickly diffusing materials having a diffusion coefficient    greater than about 10-7 cm2/sec at 50° C., such as acetophenone and    trimethylmethoxysilane or other high diffusivity materials disclosed    in the above cited U.S. Pat. No. 5,372,841. Such materials impart    short-term performance (reactive performance) (generally, 0 to about    12 months).-   Class M—Moderately diffusing materials having a diffusion    coefficient greater than about 10⁻⁸ cm²/sec, but less than about    10⁻⁷ cm²/sec at 50° C., such as phenylmethyldimethoxysilane and    p-tolylethylmethyldimethoxysilane. Such materials impart medium-term    performance (proactive performance) (generally about 12 to about 120    months).-   Class S—Slowly diffusing materials or low solubility materials, as    discussed above, having a low solubility of about 0.0001 to about    0.02 gram/cm³ at 25° C. or having a diffusivity less than about 10⁻⁸    cm²/sec at 50° C., and having a permeability less than about 10⁻¹⁰    g/cm² at 25° C., each property being measured in the insulation    material, such as cyanobutylmethyldimethoxysilane,    cyanoethylmethyldimethoxysilane and    cyanopropylmethyldimethoxysilane. Such materials impart long-term    (preemptive) performance (generally greater than about 120 months).

A “Tailored Injection” method is illustrated in FIG. 8 with a spiralschematic, and summarizes the impact of each of these eight variablesand also provides an overview of the optimization methodology of thepresent method. The prior art single formulation approach is an inherentcompromise which attempts to balance the eight parameters but must maketrade-offs between them. The inventors of the present method incorporatethe above described method for treating electrical cable at sustainedelevated pressure as a tool which provides a new degree of freedom informulation which removes many of the constraining compromises requiredby the prior art approaches. The above described method for treatingelectrical cable at sustained elevated pressure encompasses the last twosteps in the “Tailored Injection” spiral, namely “Adjust pressure” and“Optimize formulation.”

Disadvantages of the prior art methods which are mitigated or eliminatedwith the present method for selecting formulations to treat electricalcables include:

-   -   (1) The addition of trimethylmethoxysilane (a Class Q compound)        as suggested by U.S. Pat. No. 5,372,841 improves the short-term        performance at the expense of longer term performance and        significantly increases the vapor pressure and the flammability        of the mixture.    -   (2) There are no provisions for preemptive or long-term        performance. This prior art disadvantage along with the first        are discussed extensively in the above described method for        treating electrical cable at sustained elevated pressure.    -   (3) The reliance on a single formulation does not accommodate        substantial temperature differences (ΔT) or geometry differences        between cables.

The three input parameters, namely cable geometry, temperature, and ΔTare uncontrollable parameters which constrain the formulation choices.In the discussion which follows, each of these three input parameters isdescribed in detail and strategies which may be employed to compensatefor the constraints they represent are provided.

Cable Geometry

In one sense, the cable geometry was chosen by the circuit owner severaldecades prior to treatment when it was placed in the ground. In anothersense, the above described method for treating electrical cable atsustained elevated pressure allows the alteration of that geometry bythe application of pressure. As demonstrated above, while the startinggeometry and the volume in the interstitial spaces of the strands isunchangeable, the annulus between the strand bundle and the conductorshield can be increased with increasing pressure, and most unexpectedlyadditional fluid can be adsorbed within the conductor shield itself.This alteration of the cable's geometry and permeation is represented bythe last two steps in the “Tailored Injection” spiral shown in FIG. 8,namely “Adjust pressure” and “Optimize formulation.”

Anticipated Cable Temperature

Cables are well known in the art to operate over a wide range oftemperatures. Low temperatures are often the ambient ground temperatureat approximately 1 meter in depth. This temperature typically rangesfrom 0° C. in cryic soil regimes common for example in Canada andScandanaiva to 28° C. in hyperthermic soil regimes common for example inNorthern Australia, Florida, South Texas, and the low deserts ofArizona, and when the cables are lightly loaded, the cables are veryclose to uniformly at ground temperature. High temperatures for XLPEcable may include conductor temperatures approaching their maximumconductor design temperature of 90° C. For all practical purposes, thetemperature of the conductor shield will be very close to that of theconductor. The insulation, however, will have a temperature profileacross its radius and the typical profile will be a function of theambient soil temperature and the thermal conductivity of the soil. Thisgeneralization is sufficiently accurate for the most common case ofsingle-phase direct-buried cable; however, for cables in conduits orcables buried in common trenches in close proximity with each other orduct banks, more complex calculations, well known in the art, areutilized to calculate temperature profiles. Permeation is the product ofdiffusivity and solubility. Data available in the prior art demonstratethat permeability changes by over an order of magnitude over a range ofapproximately 40° C. (see “Injection Supersaturation,” Minutes of the104^(th) Meeting of the IEEE, PES, ICC, Oct. 26, 1998, AppendixA(5-30)-1, which states that “At room temperature,[phenylmethyldimethoxysilane monomer] would take 16 months to penetrate175 mils of insulation. At 60° C., [phenylmethyldimethoxysilane monomer]would require about two months to penetrate the same 175 mils.”). Thediffusion coefficients for the monomer (phenylmethyldimethoxysilane, AClass M material used in the prior art) and the oligomers(HO(PhMeSiO)_(x)H, where x=2−5) are plotted in the “DiffusionCoefficients f(T)” graph shown in FIG. 9. All values in FIG. 9 are fromU.S. Pat. No. 5,372,841, Table 3. It is clear that even greatertemperature fluctuations are possible and hence permeation rates of upto two orders of magnitude must be accommodated. Unlike the prior artone-size-fits all approach, the present method for selectingformulations ascertains the temperature profiles which are likely to beexperienced by the cable to be treated over its anticipated life and theformulation is modified to match the geometry, temperature and requiredperformance. The average temperature profile and temperature cyclingprofile are considered along with the five Ps of performance and thecable geometry. While the diffusion coefficients of the prior artmaterials are generally appropriate for average cable temperatures below15° C., the same treatment which might last 15 years at that temperaturewould be depleted after about 2 years at 60° C. The present method forselecting formulations alters the formulation in the 60° C. case tofavor Class S materials which have diffusion coefficients approximately10 to 100 times lower.

As a non-limiting example of the forgoing, consider Example 1 of theabove described method for treating electrical cable at sustainedelevated pressure where the goal was to provide the optimum treatmentfor 1000 feet of concentric 1/0, 100% XLPE insulation. Unstated in thatexample were the criteria of the present method and it was assumed thatthe temperature (25° C.) and performance requirements were typical forsuch a cable. The formulation for that case is reproduced in the tablebelow. Wt. of Aceto- Mixture phenone VMB S1 S2 Specific component massin 8.26 1.50 5.26 0.75 0.75 insulation Specific component mass in 3.910.56 2.97 0.19 0.19 conductor shield Total Component Mass 12.17 2.068.23 0.94 0.94

If the same cable design anticipated a typical temperature of 50° C.,the present method for selecting formulations teaches an entirelydifferent formulation. For this example, assume constant solubilitybetween 25° C. and 50° C. and the following diffusivities of the 4formulation components as shown in the first table below, wherein thethermal acceleration factor is ratio of diffusivity at 50° C. to that at25° C. Actual diffusion coefficients and actual solubility over thetemperature range of interest can be easily measured for each componentof interest. At the higher temperature of 50° C., the formulation in thetable above would lose its short-term, medium-term, and long-termefficacy, as shown by the “Reliable Life@50° C. (months)” column in thesecond table, below.

Based on accelerated life testing under the low temperature scenario,the acetophenone is anticipated to provide reliable performance forabout 12 months. The VMB provides reliable performance fromapproximately 9 months to 12 years (144 Thermal Diffusivity @Diffusivity @ Acceleration Material 25° C. (cm²/sec) 50° C. (cm²/sec)Factor Acetophenone 2.9 × 10⁻⁹  1.3 × 10⁻⁷ 45 VMB 3.6 × 10⁻⁹  3.1 × 10⁻⁸8.6 S1 1.6 × 10⁻¹⁰ 2.6 × 10⁻⁹ 16 S2 9.1 × 10⁻¹¹ 1.1 × 10⁻⁹ 12

months). S1 and S2 together are anticipated to provide reliableperformance from 6 to 50 years (72-600 months). Dividing each of theseperformance time periods by the thermal acceleration factor in the abovetable yields new values as outlined in the table below. ReliableReliable Life @ 25° C. Life @ 50° C. Material (months) (months)Acetophenone 0-12  0-0.3 VMB  9-144 1-17 S1/S2 72-600 4.5-50  

Obviously the reliability expectations at 50° C. are unacceptable in theshort-term (the 20-day gap between acetophenone depletion and VMBeffectiveness) and the long-term (50 months or 4.2 years). The presentmethod for selecting formulations (taken together with the abovedescribed method for treating electrical cable at sustained elevatedpressure) teaches the two options available to assure the reliabilityover a definable life-span:

-   -   1. Provide more than the saturation level of components in order        to extend the reliable life within the realm in which the        individual component performs. There are four broad cases, where        cables can be provided with an excess quantity of fluid above        the saturation level without any risk of failure caused by        supersaturation or over saturation. (1) The cable is unlikely to        have prolonged or significant temperature cycling. (2) The        compound has a solubility of less than 0.02 g/cm³ at 50° C. in        the insulation. (3) The compound change in solubility between        the highest typical temperature and lowest typical temperature        is less than 4. The change in solubility is defined as the        solubility (mass/unit volume) at the highest temperature to be        encountered in typical operation, S_(high) divided by the        solubility at the lowest temperature to be encountered in        typical operation to be encountered, S_(low). (4). The diffusion        coefficient is greater than approximately 10⁻⁶ cm²/sec at 50° C.        -   a. This may be accomplished by increasing the pressure to            accommodate more fluid.        -   b. This may be accomplished by increasing the ratio of one            component which is more desirable at the expense of a second            less critical component.    -   2. Choose a different material or materials with different        solubility and diffusivity characteristics with similar or        superior restorative effects. The new material may be used to        substitute for all or a portion of the component which may cause        supersaturation or over saturation.

As is readily recognized by someone skilled in the art, there are avariety of physical, chemical and electrical effects know to improvecable performance. The following is a partial list of the most importantknown restorative effects:

-   -   1. Water scavenging    -   2. Void filling    -   3. Dielectric stress grading    -   4. UV absorption    -   5. Partial Discharge (PD) suppression (inception and extinction)

Also readily appreciated by someone skilled in the art is theportability of these effects by their inclusion as ligand functionalityin a larger treatment molecule particularly a silane, which is itselfpart of cocktail of materials.] The following are non-limiting examplesof the virtually infinite number of possibilities:

-   -   A high dielectric nitrile or cyano group can be attached to a        alkoxysilane to make an efficacious stress grading and water        scavenging fluid.    -   3-methylbenzophenone is a larger analog of acetophenone and will        have lower permeability but will have similar UV absorption        effects, similar dielectric stress grading, and similar PD        suppression.    -   A siloxane dimer with two water reactive ligands could be        substituted for an analogous silane monomer with two water        reactive ligands to lower the solubility and the diffusion        coefficient without losing void filling, dielectric stress        grading, UV absorption, or PD suppression characteristics, and        compromising water scavenging by only 40%. (e.g.,        MeO—Si(Me)(Ph)—O—Si(Me)(Ph)—OMe is the analogous dimer of the        monomer PhMeSi(OMe)₂.)

As a non-limiting example, reliable performance comparable to the 25° C.results in the forgoing example could be obtained at 50° C. by makingthe following specific changes shown in the table below: (1) Substitute3-methylbenzophenone for acetophenone in the formulation to increase thereliable life in the short-term realm, (2) substitute a partialhydrolyzate of VMB (designated as VMB^(ph)) to decrease the permeationrate by a factor of 4 to 9, and (3) substitute high temperature analogsof both S1 and S2 (S1-ht and S2-ht) having diffusion coefficientsapproximately 16 and 12 times lower, respectively. For this example itis assumed that 3-methylbenzophenone has a permeation rate approximatelyone-third that of acetophenone. There are a variety of aromatic ketoneswhich might be used to tailor the permeation rate and provide suitablepartial discharge extinction. Mixture Methylbenzophenone VMB^(ph) S1-htS2-ht Specific 8.26 1.50 5.26 0.75 0.75 component mass. in insulationSpecific 3.91 0.56 2.97 0.19 0.19 component mass in conductor shieldTotal 12.17 2.06 8.23 0.94 0.94

There is a virtually infinite number of formulation combinations whichcan be devised to meet the performance requirements. The precedingexample is but a single manifestation of those varied possibilities.

ΔT

The geometry of the cable, the thermal conductivity of the soil and thechange in load (amperes) on a cable determines how dramatic temperaturechanges in the cable are. The load for most cables is seasonal and infact highly variable throughout a given day. Thus, for warm climateareas the maximum seasonal cable loads are generally experienced in thesummer when air-conditioner loads are the greatest. For cold climateareas the maximum cable loads are generally experienced in the winterwhen the outside temperatures are lowest. Similarly, on a typical Julyday in Austin, Tex. for example, the maximum load is reached at 4:00 PMand sinks to its minimum load at 4:00 AM. Each locale has its own uniqueload profile. Furthermore, even within a given circuit, the minimum andmaximum loads vary considerably. Consider for example the typical 1/0URD circuit which starts at a pole and travels underground connecting 10transformers in series. If each transformers load at 4:00 PM is 15amperes, the cable from the pole to the first transformer (Cable 1) iscarrying 10 transformers×15 amperes or 150 amps. The conductor of Cable1 is likely to be in the 60-80° C. range at 4:00 PM. These types ofcalculation are well know in the art and are referred to as ampacitycalculations. One source for such calculations is IEEE—IPCEA Power CableAmpacities for Copper & Aluminum Conductors, published jointly in 1962by the IEEE and the IPCEA (IEEE S-135; IPCEA P-46-426). Contrast Cable 1to the last cable (Cable 10) which serves only a single transformer andhence carries only 15 amperes of current and is likely to have aconductor temperature of approximately 25-30° C. Not only do the maximumand minimum temperature changes affect this ΔT, they also have an effecton the average anticipated temperature profile previously described.While the prior art approach would treat all ten of these cablesidentically, the present method teaches that the formula should bevaried along the length of this example circuit. Cable 10 would notexperience significant changes in temperature (ΔT) and hence there wouldbe no constraint on the maximum solubility or maximum concentration ofany single component. On the other hand for Cable 1, where theanticipated ΔT of the conductor is approximately 40° C. and theanticipated maximum ΔT for the insulation is just less than 40° C., theformulation would have to be either:

-   -   Composed entirely of components wherein the sum of the        solubilities within each class in the insulation and the shield        is less than 2% by weight at 25° C., or    -   Those components with solubility greater than 2% would have to        be limited in the formulation such that they, and any other        sister components in the same class, could not exceed 2% by        weight in the insulation.

The insulation will generally be cooler than the conductor temperature;however the insulation closest to the conductor will be just slightlylower (perhaps 1° C.) than the conductor temperature.

It should be noted that in each case the anticipated ΔT is within thetimeframe that the class of materials will be present. For example, withCable 1 above, a Class Q material which is only going to be around forsix months post-injection may be introduced above 2% in the month ofNovember in Austin, Tex. since the maximum contemplated ΔT for Novemberthrough April is less than 20° C. These rules are generalized in thefollowing formula.C _(max)=0.05−0.0006·ΔTWhere,

-   -   C_(max) is the maximum concentration as a weight fraction        (solubility and/or maximum solute) within each material class        during the time period where the material class is present at or        above the threshold concentration;    -   ΔT is the maximum change in insulation temperature, which is        generally just slightly lower than the maximum change in        conductor temperature, and ΔT is between of 0 and 75° C.    -   0.05 and 0.0006 are empirical constants determined from        experiments and information available in the art for typical        cross-linked polyethylene cables. Other empirical constants        could be substituted for other cases without departing from the        spirit of the present method.

For example, suppose ΔT is 50° C., C_(max)=0.05−0.0006·ΔT would equal0.05−0.0006·50 or 0.02 weight fraction or 2%_(w) of each material class.

Post-Failure Performance

If a circuit owner is treating cables to extend their life well beforethey have actually failed, there is little reason to supply Class Qperformance enhancing materials. This customer treatment strategy iscalled proactive if there have been a few isolated failures in cablesbeing treated or it is preemptive if there have been no failures.Lowering the amount of Class Q materials allows either Price saving oran increase in the amount of Class M and Class S materials supplied tothe cable which will extend the cable's long-term performance. The priorart approach provides the same ratio of Class Q materials to Class Mmaterials without regard to the circuit owners desires. The presentmethod simply asks the circuit owner whether they are concerned aboutshort-term post injection failures or not and then adjusts the Class Qmaterials as shown in the table below: Customer expectation Class QSupply There is no chance of post injection failure Do not use Class Qmaterials. There is little chance of post injection Use 50% of themaximum failure as this cable has been failure free. allowable Class Qmaterial(s) unless constrained by other considerations. The cable inquestion has failed more Use 75% of the maximum than 120 days prior totreatment allowable Class Q material(s) unless constrained by otherconsiderations. The cable in question has failed within the Use Class Qmaterial(s) up the last 120 days and another failure in the maximumallowable as short term is quite likely constrained by otherconsiderations.

It is possible that there are other nuances which place a particularcable between the four categories outline above and it is not adeparture from the present method to interpolate between the fouridentified cases.

Proactive Performance

If a circuit owner is treating cables preemptively well before any cablefailures are anticipated, lowering the amount of Class Q materials andClass M materials allows either Price saving or an increase in theamount of Class S materials supplied to the cable which will extend thecable's long-term performance. The prior art approach provides the sameratio of Class Q materials to Class M materials without regard to thecircuit owners desires. The present method for selecting formulationssimply asks the circuit owner whether they are concerned about mediumterm reliability or not and then adjusts the Class Q and Class Mmaterials as shown in the table below: Customer expectation Class QSupply The cable is likely to provide Do not use Class Q materials.reliable performance for 2 years. The cable is likely to provide Do notuse Class Q materials. Use 50% of reliable performance the maximumallowable Class M materials for 5 years. unless constrained by otherconsiderations, or decrease the average permeation of the Class Mmaterial(s) by a factor of approximately 2. The cable is likely toprovide Do not use Class Q materials. Use 25% of reliable performancethe maximum allowable Class M materials for 10 years. unless constrainedby other considerations. Decrease the average permeation of the Class Mmaterial(s) by a factor of approximately 4. The cable is likely toprovide Do not use Class Q materials. Do not use reliable performanceClass M materials. for 15 years.

It is possible that there are other nuances which place a particularcable between the four categories outlined above and it is not adeparture from the present method to interpolate between the fouridentified cases.

Preemptive Performance

If technology and money were not an issue, circuit owners would desireinfinite life at a very low cost. Unfortunately, both technology andmoney are an issue and preemptive performance is where the two meet.Very long life, even in excess of that provided by new cables, ispossible with the present method, particularly when it is combined withthe above described method for treating electrical cable at sustainedelevated pressure which allows a greater amount of fluid to be supplied.While the prior art approach provides the same ratio of Class Qmaterials to Class M materials and the same total amount for fluidwithout regard to the circuit owners desires, the present method forselecting formulations simply asks the circuit owner to make the valuejudgment which weighs the desired Preemptive Performance against thePrice they are willing to pay within the constraints of the cablegeometry and the available fluid technologies. This trade-off isdescribed as one element in the Price discussion which follows.

Price

Obviously, the cost of each potential restorative material can varyconsiderably depending on the ease of manufacture and scale of itscommercial availability. In addition to the direct cost of the material,the cost of handling and injection can vary depending on its physicalproperties. The circuit owner may choose to compromise preemptive (orlong-term) performance for price depending upon the circuit owner'sevaluation of the time value of money. Deferred economics principles,well described in the art (see “Recent Advances in Cable RejuvenationTechnology,” IEEE/PES Summer Meeting, 1999), are utilized to weigh theincremental cost of extended life against the incremental extended lifefor a given formulation change. For example, suppose the use ofcomponent “omega” is know to extend the reliable life of the formulationfrom 30 years to 35 years and the incremental cost for using omega overits less costly counterpart is $1.20 per foot. Is the circuit owner bestserved by utilizing omega and paying the incremental $1.20? Using theNet Present Value (NPV) analysis well known in the art, the deferredeconomics of this decision are easily determined and depend primarily onthe discount factor for future cash flows and the anticipated cost ofreplacement.

Properties

A wide variety of materials is available in the art which might aid inthe extension of reliable life of a circuit. Each of these materials hasother advantages, and disadvantages which must also be considered in theformulation decision. As non-limiting examples of this concept, it isknown in the art that certain aluminum alloys are more susceptible tocorrosion by methanol than other aluminum alloys. To the extent thecircuit owner is engaged in a process to improve the circuit reliabilitythere is little desire to introduce methanol to a cable which has asusceptible alloy. In such a case the decision maker might decrease thequantity, or even exclude, low priced and commonly used methoxy oralkoxy silanes in favor of water reactive materials which produce nomethanol or materials which are not water reactive at all. As anothercase, consider the safety aspects of including materials in theformulation having low flash points and hence high flammability. Whilethese materials may be efficacious, the safety consequences may not beallowable for certain situations, such as duct-manhole systems where theconsequences of a fire or explosion can be fatal. The prior art uses asingle active formulation for every case. The present method forselecting formulations teaches the inclusion of a wide variety ofmaterials which can meet an equally wide variety of needs and includingcircuit owner input to exclude or minimize certain kinds of materialswhich fall outside of allowable properties.

The present method for selecting formulations includes both processesand business methods which together allow the formulation to be tailoredto the end-user's requirements with far fewer compromises than the priorart approaches.

One embodiment of the present method for selecting formulations involvesinjecting insulated (solid dielectrics such as polyethylene or EPR orsolid-liquid dielectrics such as paper-oil) stranded power cables(including medium voltage, low voltage and high voltage) to provide atailored mixture of treatment materials to assure reliable life forvarious cable geometries and operational characteristics.

Another embodiment of the method for selecting formulations includesconsidering cable geometry and the anticipated temperature of a cable tovary the formulation of at least one injection compound.

The method for selecting formulations may be used where one or more ofthe following are considered to provide an optimum formulation:

-   -   a. Post-failure or short-term performance (<12 months);    -   b. Proactive or medium-term performance (12 months to 10 years);    -   c. Preemptive or long-term performance (>10 years);    -   d. Price (including fluid costs, process labor intensity, and        duration & scope of warranty);    -   e. Properties (including compatibility with aluminum or copper        conductors and flammability).

The method for selecting formulations may be employed where theanticipated temperature includes both anticipated typical temperatureand the anticipated typical temperature cycles.

The method for selecting formulations may be practiced where thevariable formulation includes injection compounds from at least twodifferent classes.

The method may also be practiced where the variable formulation includesinjection compounds from at least three different classes.

Combinations of various aspects of the method for selecting formulationsmay be utilized but for brevity are not all set forth herein.

1. A method for selecting components for a mixture to be injected intoan interstitial void volume adjacent to a central stranded conductor ofan electrical cable segment having the central conductor encased in apolymeric insulation jacket to enhance the dielectric properties of thecable segment, comprising: selecting an anticipated operatingtemperature profile for the cable segment to be used in selecting thecomponents for the mixture to be injected into the interstitial voidvolume of the cable segment; selecting a minimum desired time period tobe used in selecting the compounds for the mixture to be injected intothe interstitial void volume of the cable segment during which thedielectric properties of the cable segment are to be enhanced by themixture; selecting a first component for the mixture to provide thecable segment with a reliable life spanning a first time period for theselected operating temperature profile; selecting a second component forthe mixture to provide the cable segment with a reliable life spanning asecond time period at least in part extending beyond the first timeperiod for the selected operating temperature profile; and selecting athird component for the mixture to provide the cable segment with areliable life spanning a third time period at least in part extendingbeyond the second time period and beyond the minimum desired time periodfor the selected operating temperature profile.
 2. A method for making amixture to be injected into an interstitial void volume adjacent to acentral stranded conductor of an electrical cable segment having thecentral conductor encased in a polymeric insulation jacket to enhancethe dielectric properties of the cable segment, comprising: selecting ananticipated operating temperature profile for the cable segment to beused in selecting components for the mixture to be injected into theinterstitial void volume of the cable segment; selecting a minimumdesired time period to be used in selecting compounds for the mixture tobe injected into the interstitial void volume of the cable segmentduring which the dielectric properties of the cable segment are to beenhanced by the mixture; selecting a desired quantity of the mixture tobe injected into the interstitial void volume of the cable segment to atleast fill the interstitial void volume adjacent to a central strandedconductor of the cable segment; selecting first, second and thirdcomponents for the mixture in first, second and third quantities,respectively, to produce at least the desired quantity of the mixture tobe injected into the interstitial void volume of the cable segment,with: the first component for the mixture and the first quantity of thefirst component to be included in the mixture being further selected soas to provide the cable segment with a reliable life spanning a firsttime period for the selected operating temperature profile, the secondcomponent for the mixture and the second quantity of the secondcomponent to be included in the mixture being further selected so as toprovide the cable segment with a reliable life spanning a second timeperiod at least in part extending beyond the first time period for theselected operating temperature profile, and the third component for themixture and the third quantity of the third component to be included inthe mixture being further selected so as to provide the cable segmentwith a reliable life spanning a third time period at least in partextending beyond the second time period and beyond the minimum desiredtime period for the selected operating temperature profile; and mixingthe first, second and third quantities of the first, second and thirdcomponents together.
 3. A method for making a mixture to be injectedinto an interstitial void volume adjacent to a central strandedconductor of an electrical cable segment having the central conductorencased in a polymeric insulation jacket to enhance the dielectricproperties of the cable segment, comprising: selecting an anticipatedoperating temperature profile for the cable segment to be used inselecting components for the mixture to be injected into theinterstitial void volume of the cable segment; selecting a minimumdesired time period to be used in selecting compounds for the mixture tobe injected into the interstitial void volume of the cable segmentduring which the dielectric properties of the cable segment are to beenhanced by the mixture; selecting a desired quantity of the mixture tobe injected into the interstitial void volume of the cable segment to atleast fill the interstitial void volume adjacent to a central strandedconductor of the cable segment; selecting a first component for themixture and a first quantity of the first component to be included inthe mixture to produce a desired first concentration of the firstcomponent in the mixture so as to provide the cable segment with areliable life spanning a first time period for the selected operatingtemperature profile; selecting a second component for the mixture and asecond quantity of the second component to be included in the mixture toproduce a desired second concentration of the second component in themixture so as to provide the cable segment with a reliable life spanninga second time period at least in part extending beyond the first timeperiod for the selected operating temperature profile; selecting a thirdcomponent for the mixture and a third quantity of the third component tobe included in the mixture to produce a desired third concentration ofthe third component in the mixture so as to provide the cable segmentwith a reliable life spanning a third time period at least in partextending beyond the second time period and beyond the minimum desiredtime period for the selected operating temperature profile; and mixingthe first, second and third quantities of the first, second and thirdcomponents together.
 4. A method for making a mixture to be injectedinto an interstitial void volume adjacent to a central strandedconductor of an electrical cable segment having the central conductorencased in a polymeric insulation jacket to enhance the dielectricproperties of the cable segment, comprising: selecting an anticipatedoperating temperature profile for the cable segment to be used inselecting components for the mixture to be injected into theinterstitial void volume of the cable segment; selecting a minimumdesired time period to be used in selecting compounds for the mixture tobe injected into the interstitial void volume of the cable segmentduring which the dielectric properties of the cable segment are to beenhanced by the mixture; selecting a desired quantity of the mixture tobe injected into the interstitial void volume of the cable segment to atleast fill the interstitial void volume adjacent to a central strandedconductor of the cable segment; selecting a desired maximum price forthe desired quantity of the mixture to be injected into the interstitialvoid volume of the cable segment; selecting first, second and thirdcomponents for the mixture in first, second and third quantities,respectively, and having first, second and third prices, respectively,to produce at least the desired quantity of the mixture to be injectedinto the interstitial void volume of the cable segment with the first,second and third prices of the first, second and third components usedto produce the desired quantity of the mixture having a combined priceno greater than the desired maximum price, with: the first component forthe mixture and the first quantity of the first component to be includedin the mixture being further selected so as to provide the cable segmentwith a reliable life spanning a first time period for the selectedoperating temperature profile, the second component for the mixture andthe second quantity of the second component to be included in themixture being further selected so as to provide the cable segment with areliable life spanning a second time period at least in part extendingbeyond the first time period for the selected operating temperatureprofile, and the third component for the mixture and the third quantityof the third component to be included in the mixture being furtherselected so as to provide the cable segment with a reliable lifespanning a third time period at least in part extending beyond thesecond time period and beyond the minimum desired time period for theselected operating temperature profile; and mixing the first, second andthird quantities of the first, second and third components together. 5.A method for enhancing the dielectric properties of an electrical cablesegment having a central stranded conductor encased in a polymericinsulation jacket and having an interstitial void volume in the regionof the conductor, the method comprising: selecting an anticipatedoperating temperature profile for the cable segment to be used inselecting the components for a mixture to be injected into theinterstitial void volume of the cable segment; selecting a minimumdesired time period to be used in selecting the compounds for themixture to be injected into the interstitial void volume of the cablesegment during which the dielectric properties of the cable segment areto be enhanced by the mixture; selecting a first component for themixture to provide the cable segment with a reliable life spanning afirst time period for the selected operating temperature profile;selecting a second component for the mixture to provide the cablesegment with a reliable life spanning a second time period at least inpart extending beyond the first time period for the selected operatingtemperature profile; selecting a third component for the mixture toprovide the cable segment with a reliable life spanning a third timeperiod at least in part extending beyond the second time period andbeyond the minimum desired time period for the selected operatingtemperature profile; injecting the mixture into the interstitial voidvolume with the mixture at a pressure below the elastic limit of thepolymeric insulation jacket; and confining the mixture within theinterstitial void volume at a residual pressure greater than about 50psig, the pressure being imposed along the entire length of the cablesegment and being below the elastic limit, whereby the residual pressurewithin the void volume promotes the transport of the mixture into thepolymeric insulation jacket.
 6. The method according to claim 5 for usewith a cable segment where the central stranded conductor is surroundedby a conductor shield, wherein the mixture injected into theinterstitial void volume saturates the conductor shield and thepolymeric insulation jacket with the mixture, and wherein the mixturecontained within the interstitial void volume has a weight less than theweight of the mixture required to saturate the conductor shield and thepolymeric insulation jacket.
 7. The method according to claim 5, whereinthe mixture is supplied at a pressure greater than about 50 psig formore than about 2 hours before being confined within in the interstitialvoid volume.
 8. The method according to claim 5, wherein the pressureused in injecting the interstitial void volume is greater than theresidual pressure.
 9. The method according to claim 5, wherein theresidual pressure is about 100 psig to about 1000 psig.
 10. The methodaccording to claim 9, wherein the residual pressure is about 300 psig toabout 600 psig.
 11. A method for enhancing the dielectric properties ofan electrical cable segment having a central stranded conductor encasedin a polymeric insulation jacket and having an interstitial void volumein the region of the conductor, the cable segment having a firstclosable high-pressure connector attached at one terminus thereof and asecond closable high-pressure connector attached at another terminusthereof, each of the first and second connectors providing fluidcommunication to the interstitial void volume, the method comprising:selecting an anticipated operating temperature profile for the cablesegment to be used in selecting the components for a mixture to beinjected into the interstitial void volume of the cable segment;selecting a minimum desired time period to be used in selecting thecompounds for the mixture to be injected into the interstitial voidvolume of the cable segment during which the dielectric properties ofthe cable segment are to be enhanced by the mixture; selecting a firstcomponent for the mixture to provide the cable segment with a reliablelife spanning a first time period for the selected operating temperatureprofile; selecting a second component for the mixture to provide thecable segment with a reliable life spanning a second time period atleast in part extending beyond the first time period for the selectedoperating temperature profile; selecting a third component for themixture to provide the cable segment with a reliable life spanning athird time period at least in part extending beyond the second timeperiod and beyond the minimum desired time period for the selectedoperating temperature profile; opening both the first and secondconnectors and introducing the mixture via the first connector so as tofill the interstitial void volume; closing the second connector andintroducing an additional quantity of the mixture via the firstconnector at a pressure greater than about 50 psig, but less than theelastic limit of the polymeric insulation jacket; and closing the firstconnector so as to contain the mixture within the interstitial voidvolume at a residual pressure greater than about 50 psig, but below theelastic limit, whereby the pressure within the interstitial void volumepromotes the transport of the mixture into the polymeric insulationjacket.
 12. A method for enhancing the dielectric properties of anelectrical cable segment between first and second connectors, the cablesegment having a central stranded conductor encased in a polymericinsulation jacket and having an interstitial void volume in the regionof the conductor, the method comprising: selecting an anticipatedoperating temperature profile for the cable segment to be used inselecting the components for a mixture to be injected into theinterstitial void volume of the cable segment; selecting a minimumdesired time period to be used in selecting the compounds for themixture to be injected into the interstitial void volume of the cablesegment during which the dielectric properties of the cable segment areto be enhanced by the mixture; selecting a first component for themixture to provide the cable segment with a reliable life spanning afirst time period for the selected operating temperature profile;selecting a second component for the mixture to provide the cablesegment with a reliable life spanning a second time period at least inpart extending beyond the first time period for the selected operatingtemperature profile; selecting a third component for the mixture toprovide the cable segment with a reliable life spanning a third timeperiod at least in part extending beyond the second time period andbeyond the minimum desired time period for the selected operatingtemperature profile; filling through at least one of the first andsecond connectors the interstitial void volume along the entire lengthof the cable segment with the mixture at a pressure below the elasticlimit of the polymeric insulation jacket; and confining with the firstand second connectors the mixture within the interstitial void volume ata residual pressure selected to promote the transport of the mixtureinto the polymeric insulation jacket, with the residual pressure beingimposed along the entire length of the cable segment and being below theelastic limit.
 13. The method according to claim 12, wherein theresidual pressure at which the mixture is confined within theinterstitial void volume is sufficient to expand the interstitial voidvolume along the entire length of the cable segment by at least 5%, butbelow an elastic limit of the polymeric insulation jacket.
 14. Themethod according to claim 12, wherein the filling and confining of themixture within the interstitial void volume includes: attaching thefirst connector to a first terminus of the cable segment; attaching thesecond connector to a second terminus of the cable segment, each of thefirst and second connectors providing fluid communication to theinterstitial void volume; opening both of the first and secondconnectors and introducing the mixture via the first connector so as tofill the interstitial void volume; closing the second connector andintroducing an additional quantity of the mixture via the firstconnector at a pressure greater than about 50 psig, but less than anelastic limit of the polymeric insulation jacket; and closing the firstconnector so as to contain the mixture within the interstitial voidvolume at a residual pressure greater than about 50 psig, but below theelastic limit.
 15. A method for selecting a mixture to be injected intoan interstitial void volume adjacent to a central stranded conductor ofan electrical cable segment having the central conductor encased in apolymeric insulation jacket to enhance the dielectric properties of thecable segment, comprising: selecting an anticipated operatingtemperature profile for the cable segment to be used in selectingcomponents for the mixture to be injected into the interstitial voidvolume of the cable segment; selecting a minimum desired time period tobe used in selecting compounds for the mixture to be injected into theinterstitial void volume of the cable segment during which thedielectric properties of the cable segment are to be enhanced by themixture; selecting a desired quantity of the mixture to be injected intothe interstitial void volume of the cable segment to at least fill theinterstitial void volume adjacent to a central stranded conductor of thecable segment; and selecting first, second and third components for themixture in first, second and third quantities, respectively, to produceat least the desired quantity of the mixture to be injected into theinterstitial void volume of the cable segment, with: the first componentfor the mixture and the first quantity of the first component to beincluded in the mixture being further selected so as to provide thecable segment with a reliable life spanning a first time period for theselected operating temperature profile, the second component for themixture and the second quantity of the second component to be includedin the mixture being further selected so as to provide the cable segmentwith a reliable life spanning a second time period at least in partextending beyond the first time period for the selected operatingtemperature profile, and the third component for the mixture and thethird quantity of the third component to be included in the mixturebeing further selected so as to provide the cable segment with areliable life spanning a third time period at least in part extendingbeyond the second time period and beyond the minimum desired time periodfor the selected operating temperature profile.
 16. A method forselecting a mixture to be injected into an interstitial void volumeadjacent to a central stranded conductor of an electrical cable segmenthaving the central conductor encased in a polymeric insulation jacket toenhance the dielectric properties of the cable segment, comprising:selecting an anticipated operating temperature profile for the cablesegment to be used in selecting components for the mixture to beinjected into the interstitial void volume of the cable segment;selecting a minimum desired time period to be used in selectingcompounds for the mixture to be injected into the interstitial voidvolume of the cable segment during which the dielectric properties ofthe cable segment are to be enhanced by the mixture; selecting a desiredquantity of the mixture to be injected into the interstitial void volumeof the cable segment to at least fill the interstitial void volumeadjacent to a central stranded conductor of the cable segment; selectinga first component for the mixture and a first quantity of the firstcomponent to be included in the mixture to produce a desired firstconcentration of the first component in the mixture so as to provide thecable segment with a reliable life spanning a first time period for theselected operating temperature profile; selecting a second component forthe mixture and a second quantity of the second component to be includedin the mixture to produce a desired second concentration of the secondcomponent in the mixture so as to provide the cable segment with areliable life spanning a second time period at least in part extendingbeyond the first time period for the selected operating temperatureprofile; and selecting a third component for the mixture and a thirdquantity of the third component to be included in the mixture to producea desired third concentration of the third component in the mixture soas to provide the cable segment with a reliable life spanning a thirdtime period at least in part extending beyond the second time period andbeyond the minimum desired time period for the selected operatingtemperature profile.
 17. A method for selecting a mixture to be injectedinto an interstitial void volume adjacent to a central strandedconductor of an electrical cable segment having the central conductorencased in a polymeric insulation jacket to enhance the dielectricproperties of the cable segment, comprising: selecting an anticipatedoperating temperature profile for the cable segment to be used inselecting components for the mixture to be injected into theinterstitial void volume of the cable segment; selecting a minimumdesired time period to be used in selecting compounds for the mixture tobe injected into the interstitial void volume of the cable segmentduring which the dielectric properties of the cable segment are to beenhanced by the mixture; selecting a desired quantity of the mixture tobe injected into the interstitial void volume of the cable segment to atleast fill the interstitial void volume adjacent to a central strandedconductor of the cable segment; selecting a desired maximum price forthe desired quantity of the mixture to be injected into the interstitialvoid volume of the cable segment; and selecting first, second and thirdcomponents for the mixture in first, second and third quantities,respectively, and having first, second and third prices, respectively,to produce at least the desired quantity of the mixture to be injectedinto the interstitial void volume of the cable segment with the first,second and third prices of the first, second and third components usedto produce the desired quantity of the mixture having a combined priceno greater than the desired maximum price, with: the first component forthe mixture and the first quantity of the first component to be includedin the mixture being further selected so as to provide the cable segmentwith a reliable life spanning a first time period for the selectedoperating temperature profile, the second component for the mixture andthe second quantity of the second component to be included in themixture being further selected so as to provide the cable segment with areliable life spanning a second time period at least in part extendingbeyond the first time period for the selected operating temperatureprofile, and the third component for the mixture and the third quantityof the third component to be included in the mixture being furtherselected so as to provide the cable segment with a reliable lifespanning a third time period at least in part extending beyond thesecond time period and beyond the minimum desired time period for theselected operating temperature profile.
 18. A method for selecting atleast one dielectric property-enhancing fluid to be injected into aninterstitial void volume adjacent to a central stranded conductor of anelectrical cable segment having the central conductor encased in apolymeric insulation jacket to enhance the dielectric properties of thecable segment, comprising: selecting an anticipated operatingtemperature profile for the cable segment to be used in selecting the atleast one dielectric property-enhancing fluid to be injected into theinterstitial void volume of the cable segment; selecting a minimumdesired time period to be used in selecting the at least one dielectricproperty-enhancing fluid to be injected into the interstitial voidvolume of the cable segment during which the dielectric properties ofthe cable segment are to be enhanced by the at least one dielectricproperty-enhancing fluid; selecting the at least one dielectricproperty-enhancing fluid to provide the cable segment with a reliablelife spanning at least the minimum desired time period for the selectedoperating temperature profile.
 19. The method according to claim 18,wherein selecting the at least one dielectric property-enhancing fluidincludes selecting at least first and second components for a mixture tobe injected into the interstitial void volume of the cable segment, withthe first component for the mixture to provide the cable segment with areliable life spanning a first time period for the selected operatingtemperature profile, and the second component for the mixture to providethe cable segment with a reliable life spanning a second time period atleast in part extending beyond the first time period for the selectedoperating temperature profile.
 20. The method according to claim 19,wherein selecting the at least one dielectric property-enhancing fluidfurther includes selecting a third component for the mixture to beinjected into the interstitial void volume of the cable segment, withthe third component for the mixture to provide the cable segment with areliable life spanning a third time period at least in part extendingbeyond the second time period and beyond the minimum desired time periodfor the selected operating temperature profile and with the thirdcomponent being a combination of at least two constituent components,each to provide the cable segment with a reliable life spanning at leasta portion of the third time period for the selected operatingtemperature profile.
 21. The method according to claim 18, wherein theselected operating temperature profile is selected at least in partbased on the anticipated fluctuations over time of the differencebetween the anticipated operating temperature of the central conductorand the anticipated temperature of an outer portion of the polymericinsulation jacket during operation of the central conductor during atleast a portion of the minimum desired time period.
 22. A method forselecting a mixture to be injected into an interstitial void volumeadjacent to a central stranded conductor of an electrical cable segmenthaving the central conductor encased in a polymeric insulation jacket toenhance the dielectric properties of the cable segment, comprising:selecting an anticipated operating temperature profile for the cablesegment to be used in selecting components for the mixture to beinjected into the interstitial void volume of the cable segment;selecting a minimum desired time period to be used in selectingcompounds for the mixture to be injected into the interstitial voidvolume of the cable segment during which the dielectric properties ofthe cable segment are to be enhanced by the mixture; selecting a desiredquantity of the mixture to be injected into the interstitial void volumeof the cable segment; and selecting at least first and second componentsfor the mixture in first and second quantities, respectively, to produceat least the desired quantity of the mixture to be injected into theinterstitial void volume of the cable segment, with: the first componentfor the mixture and the first quantity of the first component to beincluded in the mixture being further selected so as to provide thecable segment with a reliable life spanning a first time period for theselected operating temperature profile, and the second component for themixture and the second quantity of the second component to be includedin the mixture being further selected so as to provide the cable segmentwith a reliable life spanning a second time period at least in partextending beyond the first time period for the selected operatingtemperature profile.
 23. A method for selecting a mixture to be injectedinto an interstitial void volume adjacent to a central strandedconductor of an electrical cable segment having the central conductorencased in a polymeric insulation jacket to enhance the dielectricproperties of the cable segment, comprising: selecting an anticipatedoperating temperature profile for the cable segment to be used inselecting components for the mixture to be injected into theinterstitial void volume of the cable segment; selecting a minimumdesired time period to be used in selecting compounds for the mixture tobe injected into the interstitial void volume of the cable segmentduring which the dielectric properties of the cable segment are to beenhanced by the mixture; selecting a desired quantity of the mixture tobe injected into the interstitial void volume of the cable segment;selecting a first component for the mixture and a first quantity of thefirst component to be included in the mixture to produce a desired firstconcentration of the first component in the mixture so as to provide thecable segment with a reliable life spanning a first time period for theselected operating temperature profile; and selecting a second componentfor the mixture and a second quantity of the second component to beincluded in the mixture to produce a desired second concentration of thesecond component in the mixture so as to provide the cable segment witha reliable life spanning a second time period at least in part extendingbeyond the first time period for the selected operating temperatureprofile.
 24. A method for selecting a mixture to be injected into aninterstitial void volume adjacent to a central stranded conductor of anelectrical cable segment having the central conductor encased in apolymeric insulation jacket to enhance the dielectric properties of thecable segment, comprising: selecting an anticipated operatingtemperature profile for the cable segment to be used in selectingcomponents for the mixture to be injected into the interstitial voidvolume of the cable segment; selecting a minimum desired time period tobe used in selecting compounds for the mixture to be injected into theinterstitial void volume of the cable segment during which thedielectric properties of the cable segment are to be enhanced by themixture; selecting a desired quantity of the mixture to be injected intothe interstitial void volume of the cable segment; selecting a desiredmaximum price for the desired quantity of the mixture to be injectedinto the interstitial void volume of the cable segment; and selecting atleast first and second components for the mixture in first and secondquantities, respectively, and having first and second prices,respectively, to produce at least the desired quantity of the mixture tobe injected into the interstitial void volume of the cable segment withthe first and second prices of the first and second components used toproduce the desired quantity of the mixture having a combined price nogreater than the desired maximum price, with: the first component forthe mixture and the first quantity of the first component to be includedin the mixture being further selected so as to provide the cable segmentwith a reliable life spanning a first time period for the selectedoperating temperature profile, and the second component for the mixtureand the second quantity of the second component to be included in themixture being further selected so as to provide the cable segment with areliable life spanning a second time period at least in part extendingbeyond the first time period for the selected operating temperatureprofile.
 25. A method for enhancing the dielectric properties of anelectrical cable segment having a central stranded conductor encased ina polymeric insulation jacket and having an interstitial void volume inthe region of the conductor, the method comprising: selecting ananticipated operating temperature profile for the cable segment to beused in selecting at least one dielectric property-enhancing fluid to beinjected into the interstitial void volume of the cable segment;selecting a minimum desired time period to be used in selecting the atleast one dielectric property-enhancing fluid to be injected into theinterstitial void volume of the cable segment during which thedielectric properties of the cable segment are to be enhanced by themixture; selecting the at least one dielectric property-enhancing fluidto provide the cable segment with a reliable life spanning at least theminimum desired time period for the selected operating temperatureprofile; injecting the at least one dielectric property-enhancing fluidinto the interstitial void volume with the at least one dielectricproperty-enhancing fluid at a pressure below the elastic limit of thepolymeric insulation jacket; and confining the at least one dielectricproperty-enhancing fluid within the interstitial void volume at aresidual pressure greater than about 50 psig, the pressure being imposedalong the entire length of the cable segment and being below the elasticlimit, whereby the residual pressure within the interstitial void volumepromotes the transport of the at least one dielectric property-enhancingfluid into the polymeric insulation jacket.
 26. The method according toclaim 25, wherein selecting the at least one dielectricproperty-enhancing fluid includes selecting at least first and secondcomponents for a mixture to be injected into the interstitial voidvolume of the cable segment, with the first component for the mixture toprovide the cable segment with a reliable life spanning a first timeperiod for the selected operating temperature profile, and the secondcomponent for the mixture to provide the cable segment with a reliablelife spanning a second time period at least in part extending beyond thefirst time period for the selected operating temperature profile. 27.The method according to claim 26, wherein selecting the at least onedielectric property-enhancing fluid further includes selecting a thirdcomponent for the mixture to be injected into the interstitial voidvolume of the cable segment, with the third component for the mixture toprovide the cable segment with a reliable life spanning a third timeperiod at least in part extending beyond the second time period andbeyond the minimum desired time period for the selected operatingtemperature profile and with the third component being a combination ofat least two constituent components, each to provide the cable segmentwith a reliable life spanning at least a portion of the third timeperiod for the selected operating temperature profile.
 28. The methodaccording to claim 25, wherein the selected operating temperatureprofile is selected at least in part based on the anticipatedfluctuations over time of the difference between the anticipatedoperating temperature of the central conductor and the anticipatedtemperature of an outer portion of the polymeric insulation jacketduring operation of the central conductor during at least a portion ofthe minimum desired time period.
 29. The method according to claim 25for use with a cable segment where the central stranded conductor issurrounded by a conductor shield, wherein the at least one dielectricproperty-enhancing fluid injected into the interstitial void volumesaturates the conductor shield and the polymeric insulation jacket withthe at least one dielectric property-enhancing fluid, and wherein the atleast one dielectric property-enhancing fluid contained within theinterstitial void volume has a weight less than the weight of the atleast one dielectric property-enhancing fluid required to saturate theconductor shield and the polymeric insulation jacket.
 30. The methodaccording to claim 25, wherein the at least one dielectricproperty-enhancing fluid is supplied at a pressure greater than about 50psig for more than about 2 hours before being confined within in theinterstitial void volume.
 31. The method according to claim 25, whereinthe pressure used in injecting the interstitial void volume is greaterthan the residual pressure.
 32. The method according to claim 25,wherein the residual pressure is about 100 psig to about 1000 psig. 33.The method according to claim 32, wherein the residual pressure is about300 psig to about 600 psig.
 34. A method for enhancing the dielectricproperties of an electrical cable segment between first and secondconnectors, the cable segment having a central stranded conductorencased in a polymeric insulation jacket and having an interstitial voidvolume in the region of the conductor, the method comprising: selectingan anticipated operating temperature profile for the cable segment to beused in selecting at least one dielectric property-enhancing fluid to beinjected into the interstitial void volume of the cable segment;selecting a minimum desired time period to be used in selecting the atleast one dielectric property-enhancing fluid to be injected into theinterstitial void volume of the cable segment during which thedielectric properties of the cable segment are to be enhanced by themixture; selecting the at least one dielectric property-enhancing fluidto provide the cable segment with a reliable life spanning at least theminimum desired time period for the selected operating temperatureprofile; filling through at least one of the first and second connectorsthe interstitial void volume along the entire length of the cablesegment with the at least one dielectric property-enhancing fluid at apressure below the elastic limit of the polymeric insulation jacket; andconfining with the first and second connectors the at least onedielectric property-enhancing fluid within the interstitial void volumeat a residual pressure selected to promote the transport of the at leastone dielectric property-enhancing fluid into the polymeric insulationjacket, with the residual pressure being imposed along the entire lengthof the cable segment and being below the elastic limit.
 35. The methodaccording to claim 34, wherein the residual pressure at which the atleast one dielectric property-enhancing fluid is confined within theinterstitial void volume is sufficient to expand the interstitial voidvolume along the entire length of the cable segment by at least 5%, butbelow an elastic limit of the polymeric insulation jacket.
 36. Themethod according to claim 34, wherein the filling and confining of theat least one dielectric property-enhancing fluid within the interstitialvoid volume includes: attaching the first connector to a first terminusof the cable segment; attaching the second connector to a secondterminus of the cable segment, each of the first and second connectorsproviding fluid communication to the interstitial void volume; openingboth of the first and second connectors and introducing the at least onedielectric property-enhancing fluid via the first connector so as tofill the interstitial void volume; closing the second connector andintroducing an additional quantity of the at least one dielectricproperty-enhancing fluid via the first connector at a pressure greaterthan about 50 psig, but less than an elastic limit of the polymericinsulation jacket; and closing the first connector so as to contain theat least one dielectric property-enhancing fluid within the interstitialvoid volume at a residual pressure greater than about 50 psig, but belowthe elastic limit.
 37. The method according to claim 34, whereinselecting the at least one dielectric property-enhancing fluid includesselecting at least first and second components for a mixture to beinjected into the interstitial void volume of the cable segment, withthe first component for the mixture to provide the cable segment with areliable life spanning a first time period for the selected operatingtemperature profile, and the second component for the mixture to providethe cable segment with a reliable life spanning a second time period atleast in part extending beyond the first time period for the selectedoperating temperature profile.
 38. The method according to claim 34,wherein selecting the at least one dielectric property-enhancing fluidfurther includes selecting a third component for the mixture to beinjected into the interstitial void volume of the cable segment, withthe third component for the mixture to provide the cable segment with areliable life spanning a third time period at least in part extendingbeyond the second time period and beyond the minimum desired time periodfor the selected operating temperature profile and with the thirdcomponent being a combination of at least two constituent components,each to provide the cable segment with a reliable life spanning at leasta portion of the third time period for the selected operatingtemperature profile.
 39. The method according to claim 34, wherein theselected operating temperature profile is selected at least in partbased on the anticipated fluctuations over time of the differencebetween the anticipated operating temperature of the central conductorand the anticipated temperature of an outer portion of the polymericinsulation jacket during operation of the central conductor during atleast a portion of the minimum desired time period.
 40. The methodaccording to claim 34 for use with a cable segment where the centralstranded conductor is surrounded by a conductor shield, wherein the atleast one dielectric property-enhancing fluid filling the interstitialvoid volume saturates the conductor shield and the polymeric insulationjacket with the at least one dielectric property-enhancing fluid, andwherein the at least one dielectric property-enhancing fluid containedwithin the interstitial void volume has a weight less than the weight ofthe at least one dielectric property-enhancing fluid required tosaturate the conductor shield and the polymeric insulation jacket. 41.The method according to claim 34, wherein the at least one dielectricproperty-enhancing fluid is supplied at a pressure greater than about 50psig for more than about 2 hours before being confined within in theinterstitial void volume.
 42. The method according to claim 34, whereinthe pressure used in filling the interstitial void volume is greaterthan the residual pressure.
 43. The method according to claim 34,wherein the residual pressure is about 100 psig to about 1000 psig. 44.The method according to claim 43, wherein the residual pressure is about300 psig to about 600 psig.